Correct the use of RB_AUGMENT in the RB_TREE macros so that is invoked
at the root of every subtree that changes in an insert or delete, and
only once, and ordered from the bottom of the tree to the top. For
intel_gas.c, the only user of RB_AUGMENT I can find, change the
augmenting routine so that it does not climb from entry to tree root
on every call, and remove a 'tree correcting' function that can be
supplanted by proper tree augmentation.

Reviewed by: kib
Tested by: pho
Differential Revision: https://reviews.freebsd.org/D23189