Smart-http tests: Improve coverage in test t5560

Smart-http tests: Improve coverage in test t5560

Commit 34b6cb8bb ("http-backend: Protect GIT_PROJECT_ROOT from /../
requests") added the path_info helper function to test t5560 but did
not use it.  We should use it as it provides another level of error
checking.

The /etc/.../passwd case is one that is not special (and the test
fails for reasons other than being aliased), so we remove that test
case.

Also rename the function from 'path_info' to 'expect_aliased'.

Acked-by: Shawn O. Pearce <spearce@spearce.org>
Signed-off-by: Tarmigan Casebolt <tarmigan+git@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>