osbuild: use load function via the format module

Instead of importing the load, load_build functions into the osbuild
namespace and using it via that, use the load function via the module
that provides them, i.e. the formats.v1 module.

osbuild/__init__.py

@@ -8,14 +8,11 @@ The utility module `osbuild.util` provides access to common functionality
 independent of osbuild but used across the osbuild codebase.
 """
 
-from .formats.v1 import load, load_build
 from .pipeline import Assembler, Pipeline, Stage
 
 
 __all__ = [
     "Assembler",
-    "load",
-    "load_build",
     "Pipeline",
     "Stage",
 ]