Make ScriptWrappable's destructor empty in oilpan bulids

In Oilpan, we no longer need ScriptWrappable's destructor. This CL makes the destructor empty. I'll completely remove the destructor from oilpan builds in a follow-up CL.

See my comments in ScriptWrappable.h for why we can remove each line of the destructor.

BUG=340522

Review URL: https://codereview.chromium.org/362963005

git-svn-id: svn://svn.chromium.org/blink/trunk@177389 bbb929c8-8fbe-4397-9dbb-9b2b20218538