daemon: Don't include <linux/fs.h>.

As of GNU libc 2.29, <sys/mount.h> declares all the constants and
functions we need, so there's no use in including <linux/fs.h> anymore.
This silences annoying warnings like this one:

  In file included from nix/libstore/local-store.cc:32:0:
  /gnu/store/…-linux-libre-headers-4.19.56/include/linux/fs.h:108:0: warning: "MS_RDONLY" redefined
   #define MS_RDONLY  1 /* Mount read-only */

  In file included from nix/libstore/local-store.cc:28:0:
  /gnu/store/…-glibc-2.29/include/sys/mount.h:36:0: note: this is the location of the previous definition
   #define MS_RDONLY MS_RDONLY

* config-daemon.ac: Remove check for <linux/fs.h>.
* nix/libstore/build.cc: Remove conditional inclusion of <linux/fs.h>.
* nix/libstore/local-store.cc: Remove "#if HAVE_LINUX_FS_H" and
inclusion of <linux/fs.h>.

config-daemon.ac

@@ -115,9 +115,6 @@ if test "x$guix_build_daemon" = "xyes"; then
   dnl to do i686-linux builds on x86_64-linux machines.
   AC_CHECK_HEADERS([sys/personality.h])
 
-  dnl Check for <linux/fs.h> (for immutable file support).
-  AC_CHECK_HEADERS([linux/fs.h])
-
   dnl Determine the appropriate default list of substitute URLs (GnuTLS
   dnl is required so we can default to 'https'.)
   guix_substitute_urls="https://ci.guix.gnu.org"

nix/libstore/build.cc

@@ -51,11 +51,6 @@
 #include <sched.h>
 #endif
 
-/* In GNU libc 2.11, <sys/mount.h> does not define `MS_PRIVATE', but
-   <linux/fs.h> does.  */
-#if !defined MS_PRIVATE && defined HAVE_LINUX_FS_H
-#include <linux/fs.h>
-#endif
 
 #define CHROOT_ENABLED HAVE_CHROOT && HAVE_SYS_MOUNT_H && defined(MS_BIND) && defined(MS_PRIVATE) && defined(CLONE_NEWNS) && defined(SYS_pivot_root)
 

nix/libstore/local-store.cc

@@ -28,11 +28,8 @@
 #include <sys/mount.h>
 #endif
 
-#if HAVE_LINUX_FS_H
-#include <linux/fs.h>
 #include <sys/ioctl.h>
 #include <errno.h>
-#endif
 
 #include <sqlite3.h>