automoc: revert attempts to silence linker warning on macos
We've made several attempts to add a dummy symbol to mocs_compilation.cpp
when there are no automoc sources:
The last attempt derives a symbol name from the path to the source file, but that breaks reproducible builds because it is not stable w.r.t. the location of the build tree. Revert all these attempts for the 3.24 release series, and return to what 3.23 and below did. Further investigation will be needed to resolve the original issue.
Fixes: #23937 (closed)
Issue: #23551, #23823 (closed), #23823 (closed)
Backport: release