Clean up now unnecessary @GwtIncompatible from JSCompiler codebase

PiperOrigin-RevId: 707232778

Author: lauraharker

src/com/google/javascript/rhino/JSIdentifier.java

@@ -45,7 +45,6 @@
 
 package com.google.javascript.rhino;
 
-import com.google.common.annotations.GwtIncompatible;
 
 /**
  * Utility class to hold isJSIdentifier.
@@ -55,7 +54,6 @@
  * <p>IMPORTANT: As of 2018-03-09 it is still not possible to use Java 8 features in this file due
  * to limitations on some internal Google projects that depend on it.
  */
-@GwtIncompatible
 public final class JSIdentifier {
   static boolean isJSIdentifier(String s) {
     int length = s.length();

src/com/google/javascript/rhino/Node.java

@@ -45,7 +45,6 @@
 import static com.google.common.base.Preconditions.checkState;
 import static com.google.javascript.jscomp.base.JSCompDoubles.isPositive;
 
-import com.google.common.annotations.GwtIncompatible;
 import com.google.common.annotations.VisibleForTesting;
 import com.google.common.base.Ascii;
 import com.google.common.collect.ImmutableMap;
@@ -2498,7 +2497,6 @@ public final boolean isValidAssignmentTarget() {
   }
 
   @DoNotCall
-  @GwtIncompatible
   @Override
   public final Object clone() {
     throw new UnsupportedOperationException("Did you mean cloneNode?");

src/com/google/javascript/rhino/TokenUtil.java

@@ -45,17 +45,12 @@
 
 package com.google.javascript.rhino;
 
-import com.google.common.annotations.GwtIncompatible;
 import com.google.javascript.jscomp.base.Tri;
 
 /**
- * Helper methods for parsing JavaScript. These methods use unsupported features in GWT's emulation
- * of java.lang.Character.
- *
- * <p>TODO(moz): Add a GWT-compatible version in the super-source directory.
+ * Helper methods for parsing JavaScript.
  *
  */
-@GwtIncompatible("Unsupported java.lang.Character fields")
 public final class TokenUtil {
   /* As defined in ECMA.  jsscan.c uses C isspace() (which allows
    * \v, I think.)  note that code in getChar() implicitly accepts

src/com/google/javascript/rhino/dtoa/DToA.java

@@ -58,10 +58,8 @@
  ***************************************************************/
 package com.google.javascript.rhino.dtoa;
 
-import com.google.common.annotations.GwtIncompatible;
 import java.math.BigInteger;
 
-@GwtIncompatible("unnecessarily complex")
 public final class DToA {
 
   private static final int