[S470934] Back out "[antlir] label images as heavyweight"

Summary:
Adding heavyweight label to all layer_rule targets seems to introduced > 10% more fbcode continuous run jobs ..

For S470934 , backing out the labelling change. Let's sync on how to address the original issue without regressing the capacity usage..

Test Plan:
```
./run_orchestrator.py -p fbcode -h 4f4dd98604612fcc884ada7b919fc0516505c89c -s continuous -m dev -e enable_v2_target_metadata
```
https://www.internalfb.com/sandcastle/workflow/2517512191705200409

Reviewed By: epilatow

Differential Revision: D66377691

fbshipit-source-id: 94d93135ff87c09254588fae9ee42df9bda0f3d8

antlir/antlir2/bzl/image/layer.bzl

@@ -747,10 +747,6 @@ def layer(
     if not rootless:
         kwargs["labels"] = selects.apply(kwargs.pop("labels", []), lambda labels: labels + ["uses_sudo"])
 
-    # Mark images as heavyweight for CI
-    if "heavyweight" not in kwargs.get("labels", []):
-        kwargs["labels"] = kwargs.pop("labels", []) + ["heavyweight"]
-
     # Annoyingly, we can only accept target_compatible_with because we need to
     # indicate a *HARD* requirement for `os:linux`, which is impossible with
     # compatible_with, and the two cannot be mixed