Remove superfluous xo rules

Author: wooorm

index.js

@@ -68,15 +68,15 @@ function doctype(node) {
     '`doctype` should have a `name`'
   )
 
-  if (node.public != null) {
+  if (node.public !== null && node.public !== undefined) {
     assert.strictEqual(
       typeof node.public,
       'string',
       '`doctype.public` should be `string`'
     )
   }
 
-  if (node.system != null) {
+  if (node.system !== null && node.system !== undefined) {
     assert.strictEqual(
       typeof node.system,
       'string',

package.json

@@ -53,11 +53,6 @@
   "xo": {
     "prettier": true,
     "esnext": false,
-    "rules": {
-      "no-eq-null": "off",
-      "eqeqeq": "off",
-      "guard-for-in": "off"
-    },
     "ignores": [
       "hast-util-assert.js"
     ]