c++: Remove large abi-specific tests [PR 99150]

[Nathan Sidwell]

Remove the two large and incorrectly abi-specific testcases I added.
Replacement tests will be forthcoming.

        PR c++/99150
        gcc/testsuite/
        * g++.dg/modules/pr99023_a.H: Delete.
        * g++.dg/modules/pr99023_b.H: Delete.

No patch because it exceeds the ml size limit :(

--
Nathan Sidwell