gdb, gdbserver: remove WinCE support code

The support for WinCE was removed with commit 84b300de ("gdbserver:
remove support for ARM/WinCE").  There is some leftover code for WinCE
support, guarded by the _WIN32_WCE macro, which I didn't know of at the
time.

I didn't remove the _WIN32_WCE references in the tests, because in
theory we still support the WinCE architecture in GDB (when debugging
remotely).  So someone could run a test with that (although I'd be
really surprised).

gdb/ChangeLog:

	* nat/windows-nat.c: Remove all code guarded by _WIN32_WCE.
	* nat/windows-nat.h: Likewise.

gdbserver/ChangeLog:

	* win32-low.cc: Remove all code guarded by _WIN32_WCE.
	* win32-low.h: Likewise.

Change-Id: I7a871b897e2135dc195b10690bff2a01d9fac05a