manifest_xml: use a set instead of (sorted) list in projectsDiff

The logic in projectsDiff performs various operations which
suggest that a set is more appropriate than a list:
 - membership lookup ("in")
 - removal

Also, sorting can be performed on the the remaining elements at the
end (which will usually involve a much smaller number of elements).

(The performance gain is invisible in comparison to the time being
spent performing git operations).

Cosmetic chance:
 - the definition of 'fromProj' is moved to be used in more places
 - the values in diff["added"] are added with a single call to extend

Change-Id: I5ed22ba73b50650ca2d3a49a1ae81f02be3b3055
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/383434
Tested-by: Sylvain Desodt <sylvain.desodt@gmail.com>
Reviewed-by: Mike Frysinger <vapier@google.com>
Commit-Queue: Sylvain Desodt <sylvain.desodt@gmail.com>

0 files changed, 0 insertions, 0 deletions