Remove checkbuild and test from parse time goals

The tests goal is not a parse time goal.

The checkbuild goal is only a parse time goal so that it doesn't result
in a circular dependency between droid and checkbuild when
ANDROID_BUILD_EVERYTHING_BY_DEFAULT is set.  Get rid of the circular
dependency by making droid depend on droid_targets, and droid_targets
depend on the targets that are normally built for droid.  checkbuild can
then always depend on droid_targets, and droid can condtionally depend
on checkbuild without introducing a circular dependency.

Bug: 24413153
Change-Id: I231d80e05ffe321384a5efbcdf5578f86ad84da0