refactor: Removed kiln generate-osm-manifest command (#530)

Removed the code, docs and tests around kiln generate-osm-manifest
command

[TNZ-33161] - [Kiln]: Remove generate-osm-manifest command, its
corresponding code, docs and tests from Kiln repo
JIRA Link: https://vmw-jira.broadcom.net/browse/TNZ-33161
Date: 05-Mar-2025

Authored-by: Ramkumar Vengadakrishnan
<ramkumar.vengadakrishnan@broadcom.com>

Author: ram-pivot

README.md

@@ -157,7 +157,6 @@ Commands:
   fetch                    fetches releases
   find-release-version     prints a json string of a remote release satisfying the Kilnfile version and stemcell constraints
   find-stemcell-version    prints the latest stemcell version from Pivnet using the stemcell type listed in the Kilnfile
-  generate-osm-manifest    Print an OSM-format manifest.
   glaze                    Pin versions in Kilnfile to match lock.
   help                     prints this usage information
   re-bake                  re-bake constructs a tile from a bake record