IDL: Drop [PerContextEnabled] extended attribute

Source/bindings/tests/idls/core/TestPartialInterface2.idl

 /*
  * Copyright (C) 2014 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 12 matching lines @@
  * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
 [
     ImplementedAs=TestPartialInterfaceImplementation, // Conflicts with default partial interface class name
-    PerContextEnabled=PartialContextName, // Conflicts with [RuntimeEnabled]
 ] partial interface TestInterface {
     const unsigned short PARTIAL2_UNSIGNED_SHORT = 0;
 
     attribute long partial2LongAttribute;
     static attribute long partial2StaticLongAttribute;
 
     void partial2VoidMethod();
     static void partial2StaticVoidMethod();
 };