Use merge_zips instead of ziptime for resetting timestamps in jacoco outputs

ziptime doesn't support ZIP64 so it is limited to 65535 entries in
a zip file.  Use the newly added support in merge_zips to reset the
timestamp instead.

Bug: 308765940
Test: builds
Change-Id: I7bc4d8d4943e7417af1783a63ac5b5904d2aa751