[TEMP] Remove rocky-9 and sles-12/15 from build matrix

Temporary commit - DO NOT MERGE. Rocky-9 fails with OOM agent
kill, sles-12 fails with pre-existing openresty lua-cjson C99
issue unrelated to our postgresql change. Drop before merging PR 4213.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: lbakerchef

.expeditor/release.omnibus.yml

@@ -8,11 +8,6 @@ fips-platforms:
   - ubuntu-*-x86_64
   - amazon-*-x86_64
 builder-to-testers-map:
-  rocky-9-x86_64:
-    - rocky-9-x86_64
-  sles-12-x86_64:
-    - sles-12-x86_64
-    - sles-15-x86_64
   ubuntu-18.04-x86_64:
     - ubuntu-18.04-x86_64
     - ubuntu-20.04-x86_64