Properly adjust pending job count.

Correctly adjust the pending job count when we start a job with multiple
Work Types.

Also remove some redundant lines and do other minor code cleanup.

Bug: 141645789
Bug: 171305774
Test: atest CtsJobSchedulerTestCases
Test: atest FrameworksMockingServicesTests:JobSchedulerServiceTest
Test: atest FrameworksServicesTests:PrioritySchedulingTest
Test: atest FrameworksServicesTests:WorkCountTrackerTest
Test: atest FrameworksServicesTests:WorkTypeConfigTest
Change-Id: I37375413ecc6dfff43686e93f7010b1c9f6e2608