gdb: Make test names unique in gdb.base/maint.exp

gdb: Make test names unique in gdb.base/maint.exp

Add prefixes or suffixes to some test names to make them unique.

Replace a send_gdb/gdb_expect with a gdb_test, and make the test name
unique.

Remove test of 'help maint' as this is already covered by a later call
to test_prefix_command_help.

Removed test of 'help maint info' and add a new call to
test_prefix_command_help instead.

gdb/testsuite/ChangeLog:

	* gdb.base/maint.exp: Make test names unique, use
	test_prefix_command_help to test 'help maint info', and remove
	repeated test of 'help maint'.