Update CleanSpec.mk for the common testcase directories.

Fix an issue with incremental builds and the new common
testcase directories.

Bug: None
Test: Removed https://android-review.googlesource.com/#/c/234478/
      then ran `m cts-platform-version-check` then reapplied the
      change to verify the failure. Then applied this new change
      to verify the problem was resolved.

Change-Id: I77529021e852af35571fb99537d87100010b47af