Revert "[scudo] seperate cache retrieval logic"

RoundedSize is supposed to be used on directly mapping. To determine if
a cached block is feasible, the size doesn't need to be rounded in
advance. As a result, the use of RoundedSize may miss some chance of
using cached blocks.

This reverts commit 4c6b8bb8.

Reviewed By: frs513

Differential Revision: https://reviews.llvm.org/D156583