[runtime] Remove useless %_IsUndetectableObject intrinsic.
Instead of using a sequence
if (something == null && !IS_UNDETECTABLE(something))) { ... }
which will be true if something is either null or undefined, it is
way simpler and way more efficient to just write
if (something === null || something === (void 0)) { ... }
instead, which allows the compiler(s) to generate pretty decent code
without any need to resort to type feedback from a CompareNil IC.
R=yangguo@chromium.org
Review URL: https://codereview.chromium.org/
1288623003
Cr-Commit-Position: refs/heads/master@{#30135}