cellular: Remove unused reference to shill-test-scripts/mm.py

BUG=chromium:404003
TEST=Trybot run on paladin, release, and chromiumos-sdk builders.

Change-Id: I449bd50ec547d1f96fbca35b32b80eff250b354d
Reviewed-on: https://chromium-review.googlesource.com/212663
Tested-by: Ben Chan <benchan@chromium.org>
Reviewed-by: Prathmesh Prabhu <pprabhu@chromium.org>
Commit-Queue: Prathmesh Prabhu <pprabhu@chromium.org>
Tested-by: Prathmesh Prabhu <pprabhu@chromium.org>
1 file changed