Remove unnecessary linux/limits.h include

None of the files affected use any macros from linux/limits.h:

    $ git grep -Fl 'NGROUPS_MAX
    ARG_MAX
    LINK_MAX
    MAX_CANON
    MAX_INPUT
    NAME_MAX
    PATH_MAX
    PIPE_BUF
    XATTR_NAME_MAX
    XATTR_SIZE_MAX
    XATTR_LIST_MAX
    RTSIG_MAX' -- src
    src/firejail/cmdline.c
    src/firejail/firejail.h
    src/libtrace/libtrace.c
    src/libtracelog/libtracelog.c

Environment:

    $ grep '^NAME' /etc/os-release
    NAME="Artix Linux"
    $ pacman -Qo /usr/include/linux/limits.h
    /usr/include/linux/limits.h is owned by linux-api-headers 5.12.3-1

Note: This include has been present on all of the affected files since
their inception.  For restrict_users.c, that's on commit 4f003da
("prevent leaking user information by modifying /home directory,
/etc/passwd and /etc/group") and for every other file, it's on commit
1379851 ("Baseline firejail 0.9.28").

Relates to netblue30#4578.

src/firejail/fs.c

@@ -23,7 +23,6 @@
 #include <sys/stat.h>
 #include <sys/statvfs.h>
 #include <sys/wait.h>
-#include <linux/limits.h>
 #include <fnmatch.h>
 #include <glob.h>
 #include <dirent.h>

src/firejail/fs_dev.c

@@ -20,7 +20,6 @@
 #include "firejail.h"
 #include <sys/mount.h>
 #include <sys/stat.h>
-#include <linux/limits.h>
 #include <glob.h>
 #include <dirent.h>
 #include <fcntl.h>

src/firejail/fs_home.c

@@ -19,7 +19,6 @@
 */
 #include "firejail.h"
 #include <sys/mount.h>
-#include <linux/limits.h>
 #include <dirent.h>
 #include <errno.h>
 #include <sys/stat.h>

src/firejail/fs_hostname.c

@@ -20,7 +20,6 @@
 #include "firejail.h"
 #include <sys/mount.h>
 #include <sys/stat.h>
-#include <linux/limits.h>
 #include <glob.h>
 #include <dirent.h>
 #include <fcntl.h>

src/firejail/fs_trace.c

@@ -20,7 +20,6 @@
 #include "firejail.h"
 #include <sys/mount.h>
 #include <sys/stat.h>
-#include <linux/limits.h>
 #include <glob.h>
 #include <dirent.h>
 #include <fcntl.h>

src/firejail/fs_var.c

@@ -20,7 +20,6 @@
 #include "firejail.h"
 #include <sys/mount.h>
 #include <sys/stat.h>
-#include <linux/limits.h>
 #include <glob.h>
 #include <dirent.h>
 #include <fcntl.h>

src/firejail/restrict_users.c

@@ -21,7 +21,6 @@
 #include "../include/firejail_user.h"
 #include <sys/mount.h>
 #include <sys/stat.h>
-#include <linux/limits.h>
 #include <fnmatch.h>
 #include <glob.h>
 #include <dirent.h>