Remove external/grub.

This project is horribly out of date, and is no longer used.

default.xml

@@ -133,7 +133,6 @@
   <project path="external/google-fonts/coming-soon" name="platform/external/google-fonts/coming-soon" />
   <project path="external/google-fonts/dancing-script" name="platform/external/google-fonts/dancing-script" />
   <project path="external/google-fonts/carrois-gothic-sc" name="platform/external/google-fonts/carrois-gothic-sc" />
-  <project path="external/grub" name="platform/external/grub" />
   <project path="external/gtest" name="platform/external/gtest" groups="pdk" />
   <project path="external/guava" name="platform/external/guava" />
   <project path="external/hamcrest" name="platform/external/hamcrest" />