test(material/slider): clean up harness testing setup (#22670)

Now that we know that the MDC-based slider won't have the same API as the non-MDC version, we can avoid sharing the test harness tests and clean up some of the logic.

Author: crisbeto

src/material-experimental/mdc-slider/testing/BUILD.bazel

@@ -24,7 +24,6 @@ ng_test_library(
         "//src/cdk/testing",
         "//src/cdk/testing/testbed",
         "//src/material-experimental/mdc-slider",
-        "//src/material/slider/testing:harness_tests_lib",
     ],
 )
 

src/material/slider/testing/BUILD.bazel

@@ -20,29 +20,18 @@ filegroup(
     srcs = glob(["**/*.ts"]),
 )
 
-ng_test_library(
-    name = "harness_tests_lib",
-    srcs = ["shared.spec.ts"],
-    deps = [
-        ":testing",
-        "//src/cdk/testing",
-        "//src/cdk/testing/testbed",
-        "//src/material/slider",
-        "@npm//@angular/forms",
-        "@npm//@angular/platform-browser",
-    ],
-)
-
 ng_test_library(
     name = "unit_tests_lib",
     srcs = glob(
         ["**/*.spec.ts"],
-        exclude = ["shared.spec.ts"],
     ),
     deps = [
-        ":harness_tests_lib",
         ":testing",
+        "//src/cdk/testing",
+        "//src/cdk/testing/testbed",
         "//src/material/slider",
+        "@npm//@angular/forms",
+        "@npm//@angular/platform-browser",
     ],
 )