Remove separate maps for function instances

Remove separate maps for function instances

ES3 specified that functions created via Function() would have
enumerable prototypes, unlike function literals.  For this reason, V8
has always had two prototypes for functions: "function_map" for
literals, and "function_instance_map" for "function instances": those
functions created by Function().

However, since 2009 or so, both maps have been the same!  Both have had
writable, non-enumerable prototypes.  Moreover, ES5 changed to specify
that function instances would have non-enumerable prototypes.

This patch removes the separate maps for function instances in sloppy
and strict mode.

R=mstarzinger@chromium.org
TEST=mjsunit/function-prototype
BUG=

Committed: 14619

[Michael Starzinger, 2013-05-10 12:27:49]

LGTM.

[wingo, 2013-05-10 12:59:48]

Committed patchset #2 manually as r14619 (presubmit successful).