remove timer.h in logging.h: logging.h does not depend on it

[guicho271828]

This is a minor contribution.

The include statement for timer.h in logging.h is unnecessary; While logging.cc uses g_timer, logging.h does not use Duration, Timer or their instances.

landmark_heuristic.cc depended on this implicit inclusion, therefore in the commit it has a new include statement.
This style is consistent with the rest of the code base which includes timer.h only when it is necessary.

[FlorianPommerening]

Sounds good but some tests are still failing. Maybe there is another explicit include missing?

[FlorianPommerening]

I don't understand the error:

/home/runner/work/downward/downward/src/search/landmarks/landmark_factory.h:26:22: error: no type named 'Timer' in namespace 'utils' [clang-diagnostic-error]

I tried to clone the code and compile locally but couldn't reproduce the error there. Also line 26 of landmark_factory.h is a comment for me. Is the branch maybe not up to date? You'd have to rebase it to the current main branch then.