[flang] Do not include dangling ac-implied-do-index in folded shape inquiry

The current code was replacing inquiry to array constructor whose
ac-value shape depends on ac-implied-do-index with an expression
using the ac-implied-do-index without the implied-do (folding the
first case added in the test as in the second case with a regular
symbol).

Differential Revision: https://reviews.llvm.org/D144655