sim: delete sim/ppc/.gdbinit

The sim/ppc/.gdbinit has existed since the initial repository creation
commits.  However, I don't think it adds any value and can be
deleted.  The contents of the file were just:

  set output-radix 16
  break error

The sim/ tree already includes rules in its Makefile to build a
.gdbinit for each simulator which sources sim/gdbinit.in, so if anyone
wants to argue for keeping either of the above lines then they should
be added to the sim/gdbinit.in file.

Keeping sim/ppc/.gdbinit in tree is an annoyance for the release
process as 'make distclean' in the sim tree ends up deleting the file.