Removing check preventing pinned stack tasks from matching by affinity.

- As of ag/1892768, we prefer matching non-affinity matching tasks,
  followed by affinity matching tasks as long as they are on the same
  display (priority from the bottom stack up). As a result, we don't need
  to exclude the pinned stack when attempting to match by affinity, as it
  can be used later when determining the match.

Bug: 37640324
Test: android.server.cts.ActivityManagerPinnedStackTests
Test: #testLaunchTaskByComponentMatchMultipleTasks
Test: #testLaunchTaskByAffinityMatchMultipleTasks
Test: #testLaunchTaskByAffinityMatchSingleTask

Change-Id: Idfe797cd51bf827876f3f0ba8ea35e1f4fcd8655