gdb: Remove previous local modification

gdb: Remove previous local modification

Due to a previous effort that saw binutils support DragonFly, the
config.bfd file no longer needs to be modified.  Unfortunately the
official binutils version wasn't modified the same way as it was in
base, so the auto-merge didn't catch that there were two versions of
each DragonFly entry.  Luckily the good version came first, so this
is simply a cleanup.

Also the README.DRAGONFLY file was updated to include a new set of
local modifications introduced with the FAKE_PROCESS_ID changes.