Deprecate -m/--mkdir from conda install

[kenodegard]

Description

There are two ways to create a new environment by listing the packages to install:

1. conda create ... (recommended and documented)
2. conda install --mkdir ... (not recommended and undocumented)

Here we remove --mkdir in favor of the more explicit conda create.

Originally introduced in conda 2.3 (see ad37b47)

Checklist - did you ...

• Add a file to the news directory (using the template) for the next release's release notes?
• Add / update necessary tests?
• Add / update outdated documentation?

[codspeed-hq]

CodSpeed Performance Report

Merging #13751 will not alter performance

_{Comparing kenodegard:deprecate-mkdir (790af2c) with main (11c21d5)}

Summary

✅ 21 untouched benchmarks

[travishathaway]

🧹