Switch clipboard_unittests to clipboard_apptests.

mojo/tools/data/unittests

 # This file contains a list of Mojo gtest unit tests.
 # This must be a valid python dictionary.
 # TODO(vtl): Add a way of specifying data dependencies instead of cacheable.
 [
   # System tests:
   {
     "test": "mojo_system_unittests",
     "run_on_android": True,
   },
 
   # Public tests:
   {
     "test": "mojo_public_bindings_unittests",
     "cacheable": False,
   },
   {
     "test": "mojo_public_environment_unittests",
   },
   {
     "test": "mojo_public_system_unittests",
   },
   {
     "test": "mojo_public_utility_unittests",
   },
 
   # Non-system, non-public tests:
   {
-    "test": "clipboard_unittests",
-  },
-  {
     "test": "mojo_application_manager_unittests",
   },
   {
     "test": "mojo_common_unittests",
   },
   {
     "test": "external_application_unittests",
   },
   {
     # These tests currently crash. We should re-enable them when they pass.
@@ skipping 23 matching lines @@
     "test": "js_services_unittests",
     "cacheable": False,
   },
 
   # Shell integration tests:
   {
     "test": "mojo_shell_tests",
     "cacheable": False,
   },
 ]