Remove broken $CONDA_DEFAULT_ENV templating engine

[kenodegard]

Checklist

• I added a descriptive title
• I searched open requests and couldn't find a duplicate

What is the idea?

Originally added in #578 (see writeup in #575) this templating engine would appear to be a precursor to the conda_build_config.yaml used today.

This templating engine is an odd artifact at this point and actually wont work anymore unless there happens to be a directory in the user's CWD that matches the currently active environment.

Per searches here on GitHub conda-forge, bioconda, nor Anaconda uses this templating engine anymore.

Uncovered while investigating #5493

Why is this needed?

Less legacy code to wrangle.

What should happen?

Review and remove clearly outdated code from the Jinja templating engine.

Additional Context

No response

[kenodegard]

The code block referenced:

conda-build/conda_build/metadata.py

Lines 1945 to 1953 in 433f048

	# search relative to current conda environment directory
	conda_env_path = os.environ.get(
	"CONDA_DEFAULT_ENV"
	) # path to current conda environment
	if conda_env_path and os.path.isdir(conda_env_path):
	conda_env_path = os.path.abspath(conda_env_path)
	conda_env_path = conda_env_path.replace("\\", "/") # need unix-style path
	env_loader = jinja2.FileSystemLoader(conda_env_path)
	loaders.append(jinja2.PrefixLoader({"$CONDA_DEFAULT_ENV": env_loader}))

[kenodegard]

Later on CONDA_DEFAULT_ENV is also set as the host_prefix within the templating engine:

conda-build/conda_build/environ.py

Line 392 in 433f048

"CONDA_DEFAULT_ENV": config.host_prefix,