Remove recycling magnificationSpec and region.

It doesn't seem like this would add a performance bump, but it does make
code quite ab it more complex (especially the prefetching CL).
Let's remove it to avoid bugs.

Test: CTSAccessibility* Tried it by hand.
Bug: 30969887
Change-Id: Ibc2fb856dbb1a0f7786882d4b89d71bbcb7e5af2