Remove libmojo.

libmojo is migrated into libchrome, so now it is almost empty and unused.
Bug: 73606903
Test: repo sync and libmojo is gone.
Change-Id: I34998ddb1a130c2f34c4e7e58ae099ab3a637476

default.xml

@@ -221,7 +221,6 @@
   <project path="external/libjpeg-turbo" name="platform/external/libjpeg-turbo" groups="pdk" />
   <project path="external/libldac" name="platform/external/libldac" groups="pdk" />
   <project path="external/libmicrohttpd" name="platform/external/libmicrohttpd" groups="pdk" />
-  <project path="external/libmojo" name="platform/external/libmojo" groups="pdk" />
   <project path="external/libmpeg2" name="platform/external/libmpeg2" groups="pdk" />
   <project path="external/libmtp" name="platform/external/libmtp" groups="pdk" />
   <project path="external/libnetfilter_conntrack" name="platform/external/libnetfilter_conntrack" groups="pdk" />