[IA] Remove recursive [de]interleaving support (#143875)
Now that the loop vectorizer emits just a single
llvm.vector.[de]interleaveN intrinsic after #141865, we can remove the
need to recognise recursively [de]interleaved intrinsics.
No in-tree target currently has instructions to emit an interleaved
access with a factor > 8, and I'm not aware of any other passes that
will emit recursive interleave patterns, so this code is effectively
dead.
Some tests have been converted from the recursive form to a single
intrinsic, and some others were deleted that are no longer needed, e.g.
to do with the recursive tree.
This closes off the work started in #139893.
