Try fixing MSVC build after r223802

LLVM_EXPLICIT is only supported by recent version of MSVC, and it seems
the not-so-recent versions get confused about the operator bool() when
tryint to resolve operator== calls.

This removed the operator bool()'s since they don't seem to be used
anyway.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@223824 91177308-0d34-0410-b5e6-96231b3b80d8