Make everyone able to modify mock package

Previously, this package was set to no owners.

However, it broke the new owner rule on gerrit.
See https://gerrit.googlesource.com/plugins/code-owners/+/master/resources/Documentation/how-to-use.md#no-code-owners-found
for details.

Test: manual
Bug: 174932174
Change-Id: I6bd2c3947cffdf7637b4c06dfb54d1b39b81e40e