module loader dead code removal and cleanups v3

[Christoph Hellwig]

Hi all,

this series removes support for long term unused export types and
cleans up various loose ends in the module loader.

Changes since v2:
 - clean up klp_find_object_symbol a bit
 - remove the now unused module_assert_mutex helper 

Changes since v1:
 - move struct symsearch to module.c
 - rework drm to not call find_module at all
 - allow RCU-sched locking for find_module
 - keep find_module as a public API instead of module_loaded
 - update a few comments and commit logs

Diffstat: