gdb/testsuite: remove some duplicate test names from guile tests

The guile support library has some "tests" that are actually being
used to setup GDB ready for the real guile tests, e.g. we load some
support modules, and define some helper functions.

As this setup is done every time we call gdb_guile_runto_main, which
could be called multiple times in a single test script, this can lead
to duplicate PASS lines.

As this setup is all pretty basic, and isn't the actual focus of the
real tests, then in this commit I pass an empty test name through to
the gdb_test_no_output calls, the result of this is that the PASS
lines are no longer printed.  This removes some duplicate tests from
the gdb.guile/*.exp set of tests.

gdb/testsuite/ChangeLog:

	* lib/guile.exp (gdb_scm_load_file): Use empty test name to
	silence PASS lines.
	(gdb_install_guile_module): Likewise.