nixos-rebuild: remove repair, never used

pkgs/os-specific/linux/nixos-rebuild/nixos-rebuild.sh

@@ -24,7 +24,6 @@ fast=
 rollback=
 upgrade=
 upgrade_all=
-repair=
 profile=/nix/var/nix/profiles/system
 buildHost=
 targetHost=
@@ -60,10 +59,6 @@ while [ "$#" -gt 0 ]; do
         upgrade=1
         upgrade_all=1
         ;;
-      --repair)
-        repair=1
-        extraBuildFlags+=("$i")
-        ;;
       --max-jobs|-j|--cores|-I|--builders)
         j="$1"; shift 1
         extraBuildFlags+=("$i" "$j")