Move ModuleMerger to namespace header_checker::linker

- Move ModuleMerger from header_checker::repr to header_checker::linker.
- Remove unused ModuleMerger::max_type_id_.

Test: development/vndk/tools/header-checker/tests/test.py
Bug: 147396457
Change-Id: Ib8ed9d1444135871f7a580fb3c5735b219dae97f
3 files changed