Remove unused _ssh_to_server from test_stamp_pattern

Commit abd154c87a75bd4100bfe72c2ed3f5d31d5cf0a2 removed the private
methods that were using _ssh_to_server so we can also remove that here
since it's now unused.

Change-Id: I31c849a2a9153fe5b93c54563b485150bc06f9c5
1 file changed