[TASK] Remove locking around log files

Log files are opened in append mode and concurrency is handled by the
operation system. The PHP documentation declares fwrite
to be atomic for normal operations.

Resolves: #56833
Releases: 6.2
Change-Id: I151fdf8ce0e237d52263ad8fbc77207fd9940633
Reviewed-on: https://review.typo3.org/28312
Reviewed-by: Markus Klein
Tested-by: Markus Klein
Reviewed-by: Oliver Klee
Reviewed-by: Georg Ringer
Tested-by: Georg Ringer