Fix equalOwnProperties

equalOwnProperties would incorrectly report two map-like objects as equal in
the case where a property defined in `left` was not defined in `right` and
whose value was considered "equal" to undefined by the equalityComparer.

This bug was found by an alert on LGTM.com

Author: s0

src/compiler/core.ts

@@ -1272,7 +1272,7 @@ namespace ts {
         if (!left || !right) return false;
         for (const key in left) {
             if (hasOwnProperty.call(left, key)) {
-                if (!hasOwnProperty.call(right, key) === undefined) return false;
+                if (!hasOwnProperty.call(right, key)) return false;
                 if (!equalityComparer(left[key], right[key])) return false;
             }
         }