Revert "[LoopVectorizer] NFCI: Calculate register usage based on TLI.getTypeLegalizationCost."
This reverts commits:
* [LoopVectorizer] NFCI: Calculate register usage based on TLI.getTypeLegalizationCost.
b873aba3.
* [LoopVectorizer] Silence warning in GetRegUsage.
9ff70110.