xtensa: fix access to the last pseudo register

xtensa: fix access to the last pseudo register

Currently access to the last pseudo register is aliased to a1. This is
done by little snippets in the beginning of xtensa_pseudo_register_read
and xtensa_pseudo_register_write that used to do such aliasing for FP
register since bdb4c075a29dd086f0868b394b488b1c94666be6, but then
FP_ALIAS was expanded into gdbarch_num_regs (current_gdbarch) +
gdbarch_num_pseudo_regs (current_gdbarch) (one register past the last
pseudo register) in 304fe2552d6e0821e8fdb7575f8e7ba6607a076d, which
then was changed to the last pseudo register in
94a0e877111421d300d26b858bd3a0a27078d1e8.

Drop these snippets.

2015-05-29  Max Filippov  <jcmvbkbc@gmail.com>
gdb/
	* xtensa-tdep.c (xtensa_pseudo_register_read)
	(xtensa_pseudo_register_write): Don't alias last pseudo register
	to a1.