TS-2384: Regression in key-lookup code between 4.0.x and 4.1.x

Revert "TS-302: Fix HTTPCacheAlt to use INK_MD5 directly instead of arrays of uin32_t. Simplify methods because of this."

This reverts commit c40c601c9167c4937f972daf7825821e527a5f67.

This breaks cache keys on certain builds. It's not clear why, but we
should remove this from 4.1.x so that we can have a stable release.