Remove 'pip install' options in recipes

[matthewfeickert]

Could you please open a ticket that describes the overarching reason we're doing this, basically what is being discussed in conda/grayskull#582? This would be for record-keeping that this is an ecosystem-wide alignment to remove the explicit pip arguments.

Originally posted by @jezdez in #5541 (comment)

As covered, in conda/grayskull#582, conda-build currently controls all pip install options through the environmental variables set in

c.f.

conda-build/conda_build/build.py

Lines 3020 to 3024 in 0ad4bb6

	env["PIP_NO_BUILD_ISOLATION"] = "False"
	# some other env vars to have pip ignore dependencies.
	# we supply them ourselves instead.
	env["PIP_NO_DEPENDENCIES"] = True
	env["PIP_IGNORE_INSTALLED"] = True

As conda-build and rattler-build both follow this pattern, it makes more sense to @henryiii and me to not make it seem to end users that they should be responsible for setting the pip install flags of --no-deps --no-build-isolation (which hides also the fact that --ignore-installed is being set as well) and that the build tools should be responsible for controlling all of this.

In conda/grayskull#584 (comment), @ocefpaf has noted there is a bug in conda-build where the

conda-build/conda_build/build.py

Lines 3020 to 3024 in 0ad4bb6

	env["PIP_NO_BUILD_ISOLATION"] = "False"
	# some other env vars to have pip ignore dependencies.
	# we supply them ourselves instead.
	env["PIP_NO_DEPENDENCIES"] = True
	env["PIP_IGNORE_INSTALLED"] = True

options don't work for multiple output feedstocks, so until the whole ecosystem shifts to rattler-build, or the conda-build bug is fixed (which they indicate is not probable), removal may be blocked.