Fix detach.exp remote check

Fix detach.exp remote check

This test seems to work with both native-gdbserver and
native-extended-gdbserver, so I removed the remote check.

When running with native-gdbserver (a stub-like target), detach makes
gdbserver stop and gdb disconnect.  runto_main just spawns a brand new
gdbserver.  So it tests the exact same thing twice.  It doesn't hurt
though.

With native-extended-gdbserver, the test is probably a bit more useful
(and similar to native).  It tests running/detaching twice using the
same gdb/gdbserver instances, since with extended-remote, you can
detach/attach/run all you want, unlike with remote.

gdb/testsuite/ChangeLog:

	* gdb.base/detach.exp: Remove is_remote check.