Prune BugreportManagerTestCases out of general-tests.

These tests define test_suite as 'general-tests' only but not used in
Test Mapping Suite. Hence, we plan to prune them to reduce size/build
time of general-tests.zip. They are listed as below:
 - BugreportManagerTestCases

Bug: 139893779

Test: m general-tests
      atest BugreportManagerTestCases

Change-Id: I093772ee5ab35f6218f2b0c7e74192ae171e05bc