The error_prone config will likely need to be updated at the same
time as the error_prone prebuilts, so move the config into the same
project. This requires jumping through some hoops because
external/error_prone may not be present in all manifests.
Bug: 64489631
Test: m -j RUN_ERROR_PRONE=true
Change-Id: I2c59df1148134ffedac0e00d32ac7082a9fb5330
