refactor(material): remove month constants from core

In the past, we accidentally published the month constants
in `@angular/material/core`. These were never intended for
public consumption but were only needed for testing. In v7,
we deprecated the constants (with the assumption that consumers
might have used constants). Now, we can remove the constants.

There is no replacement for these variables. Instead, use the zero-based
month index on your own.

BREAKING CHANGE: Deprecated month constants from `@angular/material/core` have been
removed. These have been accidentally published in the past while they
were only intended for internal consumption in tests.

Author: devversion

src/material/core/month-constants.ts

@@ -18,6 +18,3 @@ export * from './option/index';
 export * from './label/label-options';
 export * from './ripple/index';
 export * from './selection/index';
-
-// TODO(devversion): remove this with v8
-export * from './month-constants';

src/material/core/public-api.ts

@@ -15,10 +15,6 @@ export declare class AnimationDurations {
     static EXITING: string;
 }
 
-export declare const JAN = 0, FEB = 1, MAR = 2, APR = 3, MAY = 4, JUN = 5, JUL = 6, AUG = 7, SEP = 8, OCT = 9, NOV = 10, DEC = 11;
-
-export declare const JAN = 0, FEB = 1, MAR = 2, APR = 3, MAY = 4, JUN = 5, JUL = 6, AUG = 7, SEP = 8, OCT = 9, NOV = 10, DEC = 11;
-
 export interface CanColor {
     color: ThemePalette;
 }
@@ -79,8 +75,6 @@ export declare abstract class DateAdapter<D> {
     abstract today(): D;
 }
 
-export declare const JAN = 0, FEB = 1, MAR = 2, APR = 3, MAY = 4, JUN = 5, JUL = 6, AUG = 7, SEP = 8, OCT = 9, NOV = 10, DEC = 11;
-
 export declare const defaultRippleAnimationConfig: {
     enterDuration: number;
     exitDuration: number;
@@ -92,8 +86,6 @@ export declare class ErrorStateMatcher {
     static ɵprov: i0.ɵɵInjectableDef<ErrorStateMatcher>;
 }
 
-export declare const JAN = 0, FEB = 1, MAR = 2, APR = 3, MAY = 4, JUN = 5, JUL = 6, AUG = 7, SEP = 8, OCT = 9, NOV = 10, DEC = 11;
-
 export declare type FloatLabelType = 'always' | 'never' | 'auto';
 
 export declare class GestureConfig extends HammerGestureConfig {
@@ -167,18 +159,10 @@ export interface HasTabIndex {
 
 export declare type HasTabIndexCtor = Constructor<HasTabIndex>;
 
-export declare const JAN = 0, FEB = 1, MAR = 2, APR = 3, MAY = 4, JUN = 5, JUL = 6, AUG = 7, SEP = 8, OCT = 9, NOV = 10, DEC = 11;
-
-export declare const JAN = 0, FEB = 1, MAR = 2, APR = 3, MAY = 4, JUN = 5, JUL = 6, AUG = 7, SEP = 8, OCT = 9, NOV = 10, DEC = 11;
-
-export declare const JAN = 0, FEB = 1, MAR = 2, APR = 3, MAY = 4, JUN = 5, JUL = 6, AUG = 7, SEP = 8, OCT = 9, NOV = 10, DEC = 11;
-
 export interface LabelOptions {
     float?: FloatLabelType;
 }
 
-export declare const JAN = 0, FEB = 1, MAR = 2, APR = 3, MAY = 4, JUN = 5, JUL = 6, AUG = 7, SEP = 8, OCT = 9, NOV = 10, DEC = 11;
-
 export declare const MAT_DATE_FORMATS: InjectionToken<MatDateFormats>;
 
 export declare const MAT_DATE_LOCALE: InjectionToken<string>;
@@ -337,8 +321,6 @@ export declare class MatRippleModule {
     static ɵmod: i0.ɵɵNgModuleDefWithMeta<MatRippleModule, [typeof i1.MatRipple], [typeof i2.MatCommonModule, typeof i3.PlatformModule], [typeof i1.MatRipple, typeof i2.MatCommonModule]>;
 }
 
-export declare const JAN = 0, FEB = 1, MAR = 2, APR = 3, MAY = 4, JUN = 5, JUL = 6, AUG = 7, SEP = 8, OCT = 9, NOV = 10, DEC = 11;
-
 export declare function mixinColor<T extends Constructor<HasElementRef>>(base: T, defaultColor?: ThemePalette): CanColorCtor & T;
 
 export declare function mixinDisabled<T extends Constructor<{}>>(base: T): CanDisableCtor & T;
@@ -386,10 +368,6 @@ export declare class NativeDateModule {
     static ɵmod: i0.ɵɵNgModuleDefWithMeta<NativeDateModule, never, [typeof i1.PlatformModule], never>;
 }
 
-export declare const JAN = 0, FEB = 1, MAR = 2, APR = 3, MAY = 4, JUN = 5, JUL = 6, AUG = 7, SEP = 8, OCT = 9, NOV = 10, DEC = 11;
-
-export declare const JAN = 0, FEB = 1, MAR = 2, APR = 3, MAY = 4, JUN = 5, JUL = 6, AUG = 7, SEP = 8, OCT = 9, NOV = 10, DEC = 11;
-
 export interface Recognizer {
     new (options?: any): Recognizer;
     recognizeWith(otherRecognizer: Recognizer | string): Recognizer;
@@ -452,8 +430,6 @@ export interface RippleTarget {
 
 export declare type SanityChecks = boolean | GranularSanityChecks;
 
-export declare const JAN = 0, FEB = 1, MAR = 2, APR = 3, MAY = 4, JUN = 5, JUL = 6, AUG = 7, SEP = 8, OCT = 9, NOV = 10, DEC = 11;
-
 export declare function setLines(lines: QueryList<MatLine>, element: ElementRef<HTMLElement>): void;
 
 export declare class ShowOnDirtyErrorStateMatcher implements ErrorStateMatcher {