include/log: Remove timestamp and pid from log path

include/log: Remove timestamp and pid from log path

Having the timestamp and pid in the log path causes a large number of
log files to be generated, which makes it difficult to find the correct
one.
This commit removes the timestamp and pid from the log path, causing
all processes with the same name to log to the same file. To distinguish
individual processes, the log_write() function will also log the pid of
the calling process.