Remove JSFunctionResultCache.

Remove JSFunctionResultCache.

There is only one use case for it: String.prototype.search converts a
string argument into a RegExp. The cache is used to avoid repeating that
conversion. However, this does not make the added complexity worthwhile.

Review URL: https://codereview.chromium.org/1267493006

Cr-Commit-Position: refs/heads/master@{#29985}