The Smi versions of arithmetic bytecodes (AddSmi, SubSmi, MulSmi,
DivSmi, ModSmi) have a fast path for Smi case and call to a builtin
on the slow path. However, this builtin is only used by these bytecode
handlers. This cl removes the builtins and inlines them into
bytecode handlers. This will also save few checks in the slow-path.

Subtract, multiply, divide and modulus also share the same checks to 
collect type feedback on several cases. This cl also refactors them
to share the same code.

Also removed a couple of TODOs that are no longer relevant.

Bug: v8:4280, v8:6474
Change-Id: Id23bd61c2074564a1beacb0632165f52370ff226
Reviewed-on: https://chromium-review.googlesource.com/530845
Commit-Queue: Mythri Alle <mythria@chromium.org>
Reviewed-by: Igor Sheludko <ishell@chromium.org>
Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Cr-Commit-Position: refs/heads/master@{#45982}