[llvm] [SDAG][abd] Remove duplicate legality check (PR #181538)

[via llvm-commits]

================

----------------
natanelh-mobileye wrote:

done, uploaded a version where the check is just `TLI.isTypeLegal(VT)`.
RISCV shows suboptimal instruction selection (nothing too interesting: should be easy to patch).
other platforms, as I said above, do not change in significant ways

https://github.com/llvm/llvm-project/pull/181538