[CI] Stops nightly-condabuild from corrupting itself.

[Skylion007]

Motivation and Context

• Miniconda is installed, unnecessary dependencies are installed and Anaconda are installed through the installer script all corrupting each other.

How Has This Been Tested

• Should just work.

Types of changes

• Docs change / refactoring / dependency upgrade
• Bug fix (non-breaking change which fixes an issue)

Checklist

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have completed my CLA (see CONTRIBUTING)

[Skylion007]

As an aside, this logic should be merged in with a parameterized version of test-conda build so that test-conda-build actually contributes to testing the nightly build. The conda nightly build should also be parallelized across circleci.