Remove obsolete JSFunction::IsOptimizable predicate.

Remove obsolete JSFunction::IsOptimizable predicate.

This just delegates to SharedFunctionInfo::optimization_disabled and
was primarily used for assertions. Removing it due to misleading name
because already optimized functions reported being "non-optimizable".

This relands commit 181d7b85977eb752b19e1de902093783e31330ef.

R=titzer@chromium.org

Committed: https://crrev.com/eb055cb3c4a75199ad5f0a0e385c8ab817a9ff88
Cr-Commit-Position: refs/heads/master@{#28577}

[Michael Starzinger, 2015-05-21 16:30:53]

Patch Set #1: Just pure reland.
Patch Set #2: Fixed assertion.

[titzer, 2015-05-21 16:33:41]

On 2015/05/21 16:30:53, Michael Starzinger wrote:
> Patch Set #1: Just pure reland.
> Patch Set #2: Fixed assertion.

LGTM

[Michael Starzinger, 2015-05-22 09:54:31]

The CQ bit was checked by mstarzinger@chromium.org

[commit-bot: I haz the power, 2015-05-22 09:54:54]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1146423002/20001

[commit-bot: I haz the power, 2015-05-22 10:05:23]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-05-22 10:05:35]

Patchset 2 (id:??) landed as
https://crrev.com/eb055cb3c4a75199ad5f0a0e385c8ab817a9ff88
Cr-Commit-Position: refs/heads/master@{#28577}