Remove $PATH display and 'which python3.9'

The 'which' made lots of things kersplodey, since 3.9 isn't
available in most linux/mac jobs, and 'which' doesn't exist
on Windows.

Learned that 'which' returns code 1 if nothing found to match.

azure-pipelines.yml

@@ -55,10 +55,6 @@ jobs:
       - script: 'brew update -vvv && brew install fish tcsh'
         condition: and(succeeded(), eq(variables['image_name'], 'macOs'), in(variables['TOXENV'], 'py37', 'py36', 'py35', 'py34', 'py27'))
         displayName: install fish and csh via brew
-      - script: 'echo $PATH'
-        displayName: show PATH
-      - script: 'which python3.9'
-        displayName: show Python 3.9 location
     coverage:
       with_toxenv: 'coverage' # generate .tox/.coverage, .tox/coverage.xml after test run
       for_envs: [py37, py36, py35, py34, py27]