Remove unused variants of make_dynamic_error_code. NFC.

Remove unused variants of make_dynamic_error_code.  NFC.

make_dynamic_error_code was used to create a std::error_code with
a std::string message.  Now that we are migrating to llvm::Error,
there are no calls to these make_dynamic_error_code methods.

There is one single call to make_dynamic_error_code remaining, the one
inside GenericError::convertToErrorCode().  That method is only called
from File::doParse() which should be a temporary situation.  We need
to work out how to deal with File::parse() caching the error result from
doParse().  Caching errors isn't supported in the new scheme, and probably
isn't needed here, but we need to work that out.

Once thats done, dynamic error and all utilities around it can be deleted.

llvm-svn: 264982