[InstCombine] Fix multi-use handling for multi-GEP rewrite (#146689)
If we're expanding offsets for a chain of GEPs in RewriteGEPs mode, we
should also rewrite GEPs that have one-use themselves, but are kept
alive by a multi-use GEP later in the chain.
For the sake of simplicity, I've changed this to just skip the one-use
condition entirely (which will perform an unnecessary rewrite of a no
longer used GEP, but shouldn't otherwise matter).