Revert "[BasicAA] Handle two unknown sizes for GEPs"

Revert "[BasicAA] Handle two unknown sizes for GEPs"

Temporarily revert commit 8b1c4e310c2f9686cad925ad81d8e2be10a1ef3c.

After 8b1c4e310c2f the compile-time for `MultiSource/Benchmarks/MiBench/consumer-lame`
dramatically increases with -O3 & LTO, causing issues for builders with
that configuration.

I filed PR48553 with a smallish reproducer that shows a 10-100x compile
time increase.