Remove abi/cpp from the manifest

libgabi++ from abi/cpp was only useful with stlport and libstdc++,
neither of which is used in the platform any more.  The NDK has its own
copy of libgabi++, so remove the platform version.
Change-Id: I3c97a5e49c8b0e9d1269567e0c16da8b5df604aa

default.xml

@@ -17,7 +17,6 @@
     <linkfile src="root.bp" dest="Android.bp" />
     <linkfile src="bootstrap.bash" dest="bootstrap.bash" />
   </project>
-  <project path="abi/cpp" name="platform/abi/cpp" groups="pdk" />
   <project path="art" name="platform/art" groups="pdk" />
   <project path="bionic" name="platform/bionic" groups="pdk" />
   <project path="bootable/recovery" name="platform/bootable/recovery" groups="pdk" />