[clang][modules] Fix handling of `ModuleHeaderRole::ExcludedHeader`

This is a follow-up to D134224. The original patch added new `ExcludedHeader` enumerator to `ModuleMap::ModuleHeaderRole` and started associating headers with the modules they were excluded from. This was necessary to consider their module maps as "affecting" in certain situations and in turn serialize them into the PCM.

The association of the header and module needs to be handled when deserializing the PCM as well, though. This patch fixes a potential assertion failure and a regression. This essentially reverts parts of feb54b6d.

Reviewed By: Bigcheese

Differential Revision: https://reviews.llvm.org/D135381