gdb: score: drop sim file check

gdb: score: drop sim file check

There has never been a GNU/sim port for the S+Core architecture.
It was added to support private code that has (and most likely
never will) see the light of day [1].  Punt this as we don't do
this for other people.  If you want to maintain a proprietary
internal build, then that's not really our problem.

[1] https://sourceware.org/ml/gdb-patches/2009-03/msg00390.html