[stubs] Drop LoadICStub and LoadICTrampolineStub (the non-TurboFan implementations of LoadIC dispatchers).

Because of the planned improvements of IC system it does not make sense to
keep the old platform version of the stub around.

Review-Url: https://codereview.chromium.org/2418513002
Cr-Commit-Position: refs/heads/master@{#40211}