gdb: remove gdbarch_sdb_reg_to_regnum

Following the removal of the COFF debug info support,
gdbarch_sdb_reg_to_regnum is no longer used, remove it.

Change-Id: I2cb43465f1fdf74863edfa4dd00fd5f28a5a26bd
Approved-By: Andrew Burgess <aburgess@redhat.com>
5 files changed