BUG/MINOR: haproxy: Free srule->file during deinit

BUG/MINOR: haproxy: Free srule->file during deinit

Given the following example configuration:

    backend foo
    	mode http
    	use-server x if { always_true }
    	server x example.com:80

Running a configuration check with valgrind reports:

    ==18650== 14 bytes in 1 blocks are definitely lost in loss record 3 of 345
    ==18650==    at 0x4C2DB8F: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
    ==18650==    by 0x649E489: strdup (strdup.c:42)
    ==18650==    by 0x4A5438: cfg_parse_listen (cfgparse-listen.c:1548)
    ==18650==    by 0x494C59: readcfgfile (cfgparse.c:2049)
    ==18650==    by 0x5450B5: init (haproxy.c:2029)
    ==18650==    by 0x421E42: main (haproxy.c:3168)

After this patch is applied the leak is gone as expected.

This is a very minor leak that can only be observed if deinit() is called,
shortly before the OS will free all memory of the process anyway. No
backport needed.