Update ClipboardService to extend SystemService.

Test: Existing tests still passing.
      cts-tradefed run singleCommand cts-dev --module CtsTextTestCases -t android.text.cts.ClipboardManagerTest
      cts-tradefed run singleCommand cts-dev --module CtsContentTestCases -t android.content.cts.ClipboardManagerTest
      cts-tradefed run singleCommand cts-dev --module CtsDevicePolicyManagerTestCases -t com.android.cts.devicepolicy.ManagedProfileTest#testCrossProfileCopyPaste
Change-Id: Ibca156a412219f11a53f2a9250954b30b650b1aa
2 files changed