Remove BB_FEATURE_REMOUNT (small, and should always be present)

and fix documentation dependancy checks, so it is only built when
it should be built.
 -Erik

busybox.def.h

@@ -181,9 +181,6 @@
 // Enable support for a real /etc/mtab file instead of /proc/mounts
 //#define BB_FEATURE_MOUNT_MTAB_SUPPORT
 //
-// Enable support for remounting filesystems
-#define BB_FEATURE_REMOUNT
-//
 // Enable support for mounting remote NFS volumes
 //#define BB_FEATURE_NFSMOUNT
 //
@@ -236,12 +233,6 @@
 #endif
 #endif
 //
-#ifdef BB_INIT
-#ifndef BB_FEATURE_REMOUNT
-#define BB_FEATURE_REMOUNT
-#endif
-#endif
-//
 #ifdef BB_FEATURE_LINUXRC
 #ifndef BB_INIT
 #define BB_INIT