[scudo][standalone] Revert some perf-degrading changes

Summary:
A couple of seemingly innocuous changes ended up having a large impact
on the 32-bit performance. I still have to make those configurable at
some point, but right now it will have to do.

Subscribers: #sanitizers, llvm-commits

Tags: #sanitizers, #llvm

Differential Revision: https://reviews.llvm.org/D73658