Kernel+Userland: Remove the nfds entry from /sys/kernel/processes

`process.fds()` is protected by a Mutex, which causes issues when we try
to acquire it while holding a Spinlock. Since nothing seems to use this
value, let's just remove it entirely for now.

Userland/Libraries/LibCore/ProcessStatisticsReader.h

@@ -43,7 +43,6 @@ struct ProcessStatistics {
     uid_t uid;
     gid_t gid;
     pid_t ppid;
-    unsigned nfds;
     bool kernel;
     DeprecatedString name;
     DeprecatedString executable;