Revert "gdbstub: Try unlinking the unix socket before binding"

This reverts commit fccb744f41.

This commit introduced dependency of linux-user on qemu-sockets.c.
The latter includes handling of various socket types, while gdbstub
only needs unix sockets.  Including different kinds of sockets
makes it more problematic to build linux-user statically.

The original issue - the need to unlink unix socket before binding -
will be addressed in the next change.

Reviewed-by: Ilya Leoshkevich <iii@linux.ibm.com>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>

stubs/meson.build

@@ -61,8 +61,6 @@ if have_user
   if not have_system
     stub_ss.add(files('qdev.c'))
   endif
-
-  stub_ss.add(files('monitor-internal.c'))
 endif
 
 if have_system