Utilities: Use new global variables at /sys/kernel/ directory

Author: https://github.com/supercomputer7
Commit: 9d1ba0e6ad
Pull-request: https://github.com/SerenityOS/serenity/pull/15593
Reviewed-by: https://github.com/ADKaster ✅
Reviewed-by: https://github.com/kleinesfilmroellchen ✅

Userland/Utilities/mount.cpp

@@ -153,7 +153,7 @@ static ErrorOr<void> mount_all()
 static ErrorOr<void> print_mounts()
 {
     // Output info about currently mounted filesystems.
-    auto df = TRY(Core::File::open("/proc/df", Core::OpenMode::ReadOnly));
+    auto df = TRY(Core::File::open("/sys/kernel/df", Core::OpenMode::ReadOnly));
 
     auto content = df->read_all();
     auto json = TRY(JsonValue::from_string(content));