remove some inherited attributes on exceptions

These exception types are marked with `_LIBCPP_EXCEPTION_ABI` which
expands to `__attribute__((__visibility__("default")))` or
`__declspec(dllexport)`.  When building for Windows, we would hit an
error:

    cannot apply 'dllexport' to a 'dllexport' class

Remove the duplicate annotations as they will be inherited from the
class.

llvm-svn: 290785