Remove empty projects

These are the empty projects that I haven't found (merged) activity in for >6 months.

Change-Id: I79f4a89dbb716b5a403398966d44fe41ef1a6d2f
Test: treehugger

default.xml

@@ -583,7 +583,6 @@
   <project path="packages/apps/Car/Settings" name="platform/packages/apps/Car/Settings" groups="pdk-fs" />
   <project path="packages/apps/Car/Stream" name="platform/packages/apps/Car/Stream" groups="pdk-fs" />
   <project path="packages/apps/Car/SystemUpdater" name="platform/packages/apps/Car/SystemUpdater" groups="pdk-fs" />
-  <project path="packages/apps/Car/externallibs" name="platform/packages/apps/Car/externallibs" groups="pdk-fs" />
   <project path="packages/apps/Car/libs" name="platform/packages/apps/Car/libs" groups="pdk-fs" />
   <project path="packages/apps/Car/tests" name="platform/packages/apps/Car/tests" groups="pdk-fs" />
   <project path="packages/apps/CarrierConfig" name="platform/packages/apps/CarrierConfig" groups="pdk-cw-fs,pdk-fs" />
@@ -705,7 +704,6 @@
   <project path="prebuilts/manifest-merger" name="platform/prebuilts/manifest-merger" groups="pdk" clone-depth="1" />
   <project path="prebuilts/maven_repo/android" name="platform/prebuilts/maven_repo/android" groups="pdk-cw-fs,pdk-fs" clone-depth="1" />
   <project path="prebuilts/maven_repo/bumptech" name="platform/prebuilts/maven_repo/bumptech" groups="pdk-cw-fs,pdk-fs" clone-depth="1" />
-  <project path="prebuilts/maven_repo/google-play-service-client-libraries-3p" name="platform/prebuilts/maven_repo/google-play-service-client-libraries-3p" clone-depth="1" />
   <project path="prebuilts/misc" name="platform/prebuilts/misc" groups="pdk" clone-depth="1" />
   <project path="prebuilts/module_sdk/art" name="platform/prebuilts/module_sdk/art" groups="pdk" clone-depth="1" />
   <project path="prebuilts/ndk" name="platform/prebuilts/ndk" groups="pdk" clone-depth="1" />
@@ -779,7 +777,6 @@
   <project path="test/app_compat/csuite" name="platform/test/app_compat/csuite" />
   <project path="test/mts" name="platform/test/mts" />
   <project path="test/suite_harness" name="platform/test/suite_harness" groups="cts,pdk-cw-fs,pdk-fs" />
-  <project path="test/vti/alert" name="platform/test/vti/alert" groups="vts,projectarch,pdk" />
   <project path="test/vti/dashboard" name="platform/test/vti/dashboard" groups="vts,projectarch,pdk" />
   <project path="test/vti/fuzz_test_serving" name="platform/test/vti/fuzz_test_serving" groups="vts,projectarch,pdk" />
   <project path="test/vti/test_serving" name="platform/test/vti/test_serving" groups="vts,projectarch,pdk" />