[antlir] remove 'all_images_in_package_use_default_os'

Summary: This no-op function is no longer called anywhere, delete it

Test Plan:
testhard
```
[vmagro@9344.od /data/sandcastle/boxes/fbsource (f26761174)]$ buck targets fbcode//... --streaming >/dev/null
Buck UI: https://www.internalfb.com/buck2/524f098e-ff1d-4036-94ee-dcd986b55e7b
Command: targets.
Time elapsed: 0.3s
```

Reviewed By: naveedgol

Differential Revision: D68722715

fbshipit-source-id: 3e592d60d336167911d0099e129ef653d0f382da

antlir/antlir2/os/package.bzl

@@ -21,9 +21,3 @@ def set_default_os_for_package(*, default_os: str):
 
 def get_default_os_for_package() -> str:
     return read_package_value(_DEFAULT_OS_KEY) or "centos9"
-
-def all_images_in_package_use_default_os(
-        yes: bool = True):  # @unused
-    # Must still exist until the `redundant_default_os` codemod is complete and
-    # removed all callsites
-    pass