Remove Java.synchronized

* It does not work on host objects.
* It only worked on Ruby objects, for which TruffleRuby.synchronized is better.

Author: eregon

CHANGELOG.md

@@ -79,6 +79,7 @@ Changes:
 
 * Standalone builds of TruffleRuby are now based on JDK11 (they used JDK8 previously). There should be no user-visible changes. Similarly, JDK11 is now used by default in development instead of JDK8.
 * The deprecated `Truffle::System.synchronized` has been removed.
+* `Java.synchronized` has been removed, it did not work on host objects.
 
 # 21.0.0
 

doc/user/polyglot.md

@@ -128,8 +128,6 @@ To access instance methods use `.class`, such as `MyClass.class.getName`.
 
 To import a Java class as a top-level constant, use `Java.import 'name'`.
 
-`Java.synchronized(object) { }` will use the Java object's monitor to synchronize.
-
 ## Embedding in Java
 
 TruffleRuby is embedded via the Polyglot API, which is part of GraalVM.

spec/truffle/interop/java_synchronized_spec.rb

@@ -58,12 +58,6 @@ def self.import(name)
     type
   end
 
-  def self.synchronized(object)
-    TruffleRuby.synchronized(object) do
-      yield
-    end
-  end
-
   # test-unit expects `Java::JavaLang::Throwable` to be resolvable if `::Java` is defined (see assertions.rb).
   # When doing JRuby-style interop, that's a fine assumption. However, we have `::Java` defined for Truffle-style
   # interop and in that case, the assumption does not hold. In order to allow the gem to work properly, we define