Revert "[AggressiveInstCombine] Fold strcmp for short string literals"

This reverts commit 5dde7551,
cbfcf901 and
8981520b due to a miscompile introduced in
8981520b (see
https://reviews.llvm.org/D154725#4568845 for details)

Differential Revision: https://reviews.llvm.org/D157430