gdbserver: remove support for ARM/WinCE

This port has been unmaintained for years, remove it.

gdbserver/ChangeLog:

	* Makefile.in (SFILES): Remove win32-arm-low.cc, wincecompat.cc.
	* configure.srv: Remove mingw32ce cases.
	* server.h, win32-low.cc: Remove __MINGW32CE__-guarded code.
	* win32-low.h (to_back_slashes): Remove.
	* win32-arm-low.cc, wincecompat.cc, wincecompat.h: Remove.

Change-Id: Ib75c0b55b0ab7caca38bbeff5f2fa9397a8e7e8d