KWSys: Remove useless include <sys/procfs.h> (#11648)

The header was included only under "#ifdef __linux", but not all Linux
distributions provide the header.  SystemInformation uses no symbols
from this header, so do not include it.

Source/kwsys/SystemInformation.cxx

@@ -66,7 +66,6 @@
 #endif
 
 #ifdef __linux
-# include <sys/procfs.h>
 # include <sys/types.h>
 # include <unistd.h>
 # include <fcntl.h>