tests: split out manifest case from test-strip-cross.t The manifest case was added on after the other cases, in d67cfe0d4714 (test-strip-cross: test handling of linkrev crosses in the manifest, 2008-01-20). I think it's easier to read and modify if it's separated. Differential Revision: https://phab.mercurial-scm.org/D6792

tests: don't log manifest-file in test-strip-cross.t I'm confident that the file is there only to help produce a certain manifest log; there is nothing special about the file's filelog itself. (And there already is a `hg debugindex --manifest` call higher up in the file that shows the crossed linkrevs.) Differential Revision: https://phab.mercurial-scm.org/D6791