[GDBserver] Use pre-generated amd64-linux tdesc as test

Now, all these amd64-linux pre-generated tdesc can be used as test, so
don't need to build them if $development is false.

gdb/gdbserver:

2017-09-05  Yao Qi  <yao.qi@linaro.org>

	* configure.srv: Empty srv_amd64_linux_regobj if $development is
	false.
	(ipa_amd64_linux_regobj): Remove.
	(ipa_x32_linux_regobj): Remove.