remove integer sanitizer suppression in validation.cpp

Summary:
While looking at backporting core#24196, I noticed that the offending code was already changed in D359 (unsigned int -> size_t) and fixed in D1528 (removal of the for (size_t j = tx.vin.size(); j-- > 0;) loop)

Removing the file-wide suppression means that new UB can now be detected.

Test Plan:
With UBSAN
ninja && ninja check check-functional

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D12821