Consolidate reqs into top level requirements_dev.txt

[mcgibbon]

Purpose

Currently Pace has many requirements.txt files and variants. This makes it difficult to understand how the environment is managed and make changes. This PR consolidates all of them into the top level requirements files.

Infrastructure changes:

• deleted requirements files in driver examples, in each subpackage top level, and in fv3core/requirements
• deleted top level requirements.txt, as requirements.dev serves its purpose
• deleted fv3core/.jenkins/install_virtualenv.sh and modified fv3core/.jenkins/jenkins.sh to use the top-level .jenkins/install_virtualenv.sh

Checklist

Before submitting this PR, please make sure:

• [x] You have followed the coding standards guidelines established at Code Review Checklist.
• [x] Docstrings and type hints are added to new and updated routines, as appropriate
• [x] All relevant documentation has been updated or added (e.g. README, CONTRIBUTING docs)
• [x] For each public change and fix in pace-util, HISTORY has been updated
• [x] Unit tests are added or updated for non-stencil code changes

[mcgibbon]

launch jenkins

[mcgibbon]

launch jenkins

[mcgibbon]

launch jenkins

[mcgibbon]

jenkins passed other than random failures on gpu backend https://jenkins.ginko.ch/job/pace_PR/2763/

[mcgibbon]

launch jenkins

[mcgibbon]

launch jenkins

[mcgibbon]

pace-physics-regression-PR is failing on the gpu parallel tests with a segfault, failed on the last run with another intermittent error.

[mcgibbon]

launch jenkins

[mcgibbon]

launch jenkins

[mcgibbon]

launch jenkins

[mcgibbon]

launch jenkins

[mcgibbon]

launch jenkins

[mcgibbon]

OK, after enough repeated launches of jenkins, I can say this PR reproducibly causes the gt:gpu physics parallel tests to fail, and all non-numpy backends to fail to compile for fv3core.