drop GIT_STRATEGY: clone for lektor builds

no reason this is needed anymore, and it should help make some builds a
bit faster since a few repos are getting big (eg. blog)

lektor.yml

@@ -8,7 +8,6 @@ include:
 .lektor:
   image: containers.torproject.org/tpo/tpa/base-images/python:bookworm
   variables:
-    GIT_STRATEGY: clone
     GIT_SUBMODULE_STRATEGY: recursive
     PIP_CACHE_DIR: "$CI_PROJECT_DIR/.cache/pip"
   cache: