Merge #6490

6490: Minimize convert_integer_literal tests r=matklad a=m-ysk

Closes #6455

This PR removes some redundant tests around convert_integer_literal.

First, it removes test cases about converting integer with underscores except for just one case. This is because the process of removing of underscores in given integer literals is independent from radix.

Second, as well as underscore cases, it removes test cases about converting integer with suffix except for just one case. This is because the process of handling suffix is independent from radix.

Finally, it removes small decimal integer cases. This is because "special case where they return early" has been removed by the PR #6482, so we have no need to retain this cases.

Co-authored-by: m-ysk <myskjp@gmail.com>