We obsolete a handful of terms representing insect anlagen (a type of
precursor structure that differs from a primordium in that the anlage is
not yet morphologically distinguishable from the surrounding tissues).
Uberon does not need such a level of precision, so having terms for the
primordia is enough.

closes #2972

Direct anyone looking for 'insect anlage in statu nascendi' to the
generic term for 'anlage'.