Avoid including cts-system-all.api as a test module.

"cts-system-all.api" is not a test module, rather
it is a target to generate a zip file resouce needed
by other tests.

Bug: 156204418
Test: cts-tradefed run cts -m CtsSystemApiSignatureTestCases
Test: `cts-tradefed run cts -m cts-system-all.api` runs no tests.
Change-Id: I090356320899ed426ac98b7bb4b2b175c63277a6
1 file changed