Hi,
you httpd.log looks strangly big. Do you have any debugging (traceoptions) or syslog configuration for this file? On a test SRX httpd.log is only 8 kB - yours is over 1 GB!
I would suggest you to look into the content of the file and verify that you don't need it. then the file can be cleared with 'clear log httpd.log'.
If you are unsure if you need the content, then copy the file to a remote location via scp and then clear the log as stated above.