Remove synchronized from attach/disposeThread

The map is synchronized and it doesn't seem needed otherwise. It was
causing a deadlock because of locking order with GIL.

Author: msimacek

graalpython/com.oracle.graal.python/src/com/oracle/graal/python/runtime/PythonContext.java

@@ -2683,7 +2683,7 @@ public void initializeMultiThreading() {
         handler.activateGIL();
     }
 
-    public synchronized void attachThread(Thread thread, ContextThreadLocal<PythonThreadState> threadState) {
+    public void attachThread(Thread thread, ContextThreadLocal<PythonThreadState> threadState) {
         CompilerAsserts.neverPartOfCompilation();
         PythonThreadState pythonThreadState = threadState.get(thread);
         threadStateMapping.put(thread, pythonThreadState);
@@ -2723,7 +2723,7 @@ public void initializeNativeThreadState(PythonThreadState pythonThreadState) {
         }
     }
 
-    public synchronized void disposeThread(Thread thread, boolean canRunGuestCode) {
+    public void disposeThread(Thread thread, boolean canRunGuestCode) {
         CompilerAsserts.neverPartOfCompilation();
         // check if there is a live sentinel lock
         PythonThreadState ts = threadStateMapping.get(thread);