Fix the vxworks crtstuff handling of kernel/rtp variations

Fix the vxworks crtstuff handling of kernel/rtp variations

The ports that support RTPs achieve the kernel/rtp compilation
and link distinction through the multilib mechanism.

This patch just removes the bogus explicit extraneous
materialization of this distinction in the common VxWorks
configuration files and leaves the rtp specialization all
to the multilib machinery.

2020-10-15  Olivier Hainque  <hainque@adacore.com>

libgcc/
	* config/t-vxcrtstuff: Remove the -kernel/-rtp specialization.

gcc/
	* config/vxworks.h (VX_CRTBEGIN_SPEC): Likewise.