Join readmeta and lint into the same task/job

This way, the preparing commands are only run once. Also, if readmeta fails,
lint will fail with the same message. So having the two messages thrown in
parallel is of little use.

.gitlab-ci.yml

@@ -9,7 +9,4 @@ before_script:
 metadata_check:
   script:
     - fdroid readmeta
-
-metadata_lint:
-  script:
     - fdroid lint