Revert "unordered_map: Reuse insert logic in emplace when possible, NFC"
Revert "unordered_map: Reuse insert logic in emplace when possible, NFC"

This reverts commit r258575.  EricWF sent me an email (no link since it
was off-list) requesting to review this pre-commit instead of
post-commit.

git-svn-id: 756ef344af921d95d562d9e9f9389127a89a6314@258625 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/libcxx,llvm-mirror/libcxx,llvm-mirror/libcxx,llvm-mirror/libcxx,llvm-mirror/libcxx