Improve / fix documentation for affine map composition utilities - NFC

- improve/fix doc comments for affine apply composition related methods.
- drop makeSingleValueComposedAffineApply - really redundant and out of line in
  a public API; it's just returning the first result of the composed affine
  apply op, and not making a single result affine map or an affine_apply op.

PiperOrigin-RevId: 230406169