Remove getPropertyDescriptor

Reviewed by Oliver Hunt.

This is used by lookupGetter/lookupSetter - this can easily bee replaced by getPropertySlot.
Since we'll be getting the GetterSetter from the slot in the setter case, rename isGetter() to isAccessor().

* runtime/JSObject.cpp:
* runtime/JSObject.h:
    - remove getPropertyDescriptor
* runtime/ObjectPrototype.cpp:
(JSC::objectProtoFuncLookupGetter):
(JSC::objectProtoFuncLookupSetter):
    - replace call to getPropertyDescriptor with getPropertySlot
* runtime/PropertyDescriptor.h:
* runtime/PropertySlot.h:
(JSC::PropertySlot::isAccessor):
(JSC::PropertySlot::isCacheableGetter):
(JSC::PropertySlot::getterSetter):
    - rename isGetter() to isAccessor()



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@154337 268f45cc-cd09-0410-ab3c-d52691b4dbfc