Improve sanity checking of the parsed DEPS submodules

This is in preparation of updating to the new stable branch 1750
(Chromium version 33.0.1750.x)
Move the sanityCheckModules function to version_resolver.py and
check if the parsed svn refs exist in the remote git repository.
If they do not exist fall back to the git shasum we parsed from
the .DEPS.git file.
This patch also removes the unused parseFile function.

Change-Id: Ie0c11fdd9326ee87e9dcc670c0a7c26f9a498fd5
Reviewed-by: Pierre Rossi <pierre.rossi@gmail.com>