Remove unused method from MatchAllNetworkSpecifier

checkNotMatchAllNetworkSpecifier is a hidden method inside
MatchAllNetworkSpecifier, and the callers have implemented
the logic by themselves to prevent calling hidden method.
Remove it because there is no one using it.

Bug: 172183305
Test: atest FrameworksNetTests
Change-Id: I22a3a99f2b4ec6f4b57ef8867b72d48db2f0c1f6

core/java/android/net/MatchAllNetworkSpecifier.java

@@ -31,17 +31,6 @@ import android.os.Parcelable;
  */
 @SystemApi
 public final class MatchAllNetworkSpecifier extends NetworkSpecifier implements Parcelable {
-    /**
-     * Utility method which verifies that the ns argument is not a MatchAllNetworkSpecifier and
-     * throws an IllegalArgumentException if it is.
-     * @hide
-     */
-    public static void checkNotMatchAllNetworkSpecifier(NetworkSpecifier ns) {
-        if (ns instanceof MatchAllNetworkSpecifier) {
-            throw new IllegalArgumentException("A MatchAllNetworkSpecifier is not permitted");
-        }
-    }
-
     /** @hide */
     @Override
     public boolean canBeSatisfiedBy(NetworkSpecifier other) {