blivet: Remove unneccesary patching

Fixes https://github.com/NixOS/nixops/issues/552

`--cache` argument is now mandatory for `pvscan` both from hetzner rescue
system and from nixpkgs.

pkgs/development/python-modules/blivet/default.nix

@@ -28,7 +28,6 @@ in buildPythonPackage rec {
     }' blivet/formats/__init__.py
     sed -i -e 's|"lsof"|"${lsof}/bin/lsof"|' blivet/formats/fs.py
     sed -i -r -e 's|"(u?mount)"|"${utillinux}/bin/\1"|' blivet/util.py
-    sed -i -e '/pvscan/s/, *"--cache"//' blivet/devicelibs/lvm.py
   '';
 
   propagatedBuildInputs = [

pkgs/tools/filesystems/nixpart/0.4/blivet.nix

@@ -28,7 +28,6 @@ buildPythonApplication rec {
     }' blivet/formats/__init__.py
     sed -i -e 's|"lsof"|"${lsof}/bin/lsof"|' blivet/formats/fs.py
     sed -i -r -e 's|"(u?mount)"|"${utillinux.bin}/bin/\1"|' blivet/util.py
-    sed -i '/pvscan/s/, *"--cache"//' blivet/devicelibs/lvm.py
   '' + stdenv.lib.optionalString useNixUdev ''
     sed -i -e '/find_library/,/find_library/ {
       c libudev = "${systemd.lib}/lib/libudev.so.1"