libRemarks.{so,dylib}: remove Remarks.dylib.exports

Remarks.exports is only intended for NOT (BUILD_SHARED_LIBS OR LLVM_LINK_LLVM_DYLIB)
builds.

For (unintended use case) BUILD_SHARED_LIBS OR LLVM_LINK_LLVM_DYLIB (the latter
is used by some Linux distros), the library defines just one symbol on ELF.
There is no need to use a version script.

I think this is a more proper solution than D139932 and fixes `symbol not
defined` errors after lld default change D135402.