Remove isolate->GetCurrentContext from V8ErrorHandler

- This CL replaces isolate->GetCurrentContext in V8ErrorHandler::callListenerFunction with scriptState()->context(). This doesn't change any behavior because we've already entered the ScriptState before calling V8ErrorHandler::callListenerFunction.

- This CL drops an ExecutionContext* parameter from callListenerFunction because it's unused.

BUG=357144

Review URL: https://codereview.chromium.org/308343002

git-svn-id: svn://svn.chromium.org/blink/trunk@175292 bbb929c8-8fbe-4397-9dbb-9b2b20218538