Remove proc->priv->new_inferior

Remove proc->priv->new_inferior

As the result of the previous patch, new_inferior is no longer used.
This patch is to remove it.

gdb/gdbserver:

2015-07-24  Yao Qi  <yao.qi@linaro.org>

	* linux-low.c (linux_create_inferior): Remove setting to
	proc->priv->new_inferior.
	(linux_attach): Likewise.
	(linux_low_filter_event): Likewise.
	* linux-low.h (struct process_info_private) <new_inferior>: Remove.