Convert the array functions in calculateChecksum() to loops

Two changes.

The first converts the array functions in calculateChecksum() into loops.

The second was in registerCacheTagsForPreload() and is reverted. getMultiple() drains $preloadTags in the same call that fills it, so the list never grows across calls. The timing I posted for that change came from a bench that reads no checksum in between, so it does not hold.

CacheTagsChecksumTest is removed.