Remove obsolete supporting configuration

There are no longer any macOS jobs.  Delete the macOS checks.
There are no longer any coverage jobs.  Delete codecov hook.
There are no longer any pyinstaller jobs.  Delete extra pyinstaller check.

.travis.yml

@@ -12,12 +12,7 @@ env:
     - TAHOE_LAFS_HYPOTHESIS_PROFILE=ci
 
 install:
-# ~/.local/bin is on $PATH by default, but on OS-X, --user puts it elsewhere
-  - if [ "${TRAVIS_OS_NAME}" = "osx" ]; then export PATH=$HOME/Library/Python/2.7/bin:$PATH; fi
-  - if [ "${TRAVIS_OS_NAME}" = "osx" ]; then wget https://bootstrap.pypa.io/get-pip.py && sudo python ./get-pip.py; fi
-  - pip list
-  - if [ "${TRAVIS_OS_NAME}" = "osx" ]; then pip install --user --upgrade codecov tox setuptools virtualenv; fi
-  - if [ "${TRAVIS_OS_NAME}" = "linux" ]; then pip install --upgrade codecov tox setuptools virtualenv; fi
+  - pip install --upgrade tox setuptools virtualenv
   - echo $PATH; which python; which pip; which tox
   - python misc/build_helpers/show-tool-versions.py
 
@@ -25,13 +20,6 @@ script:
   - |
     set -eo pipefail
     tox -e ${T}
-    # To verify that the resultant PyInstaller-generated binary executes
-    # cleanly (i.e., that it terminates with an exit code of 0 and isn't
-    # failing due to import/packaging-related errors, etc.).
-    if [ "${T}" = "pyinstaller" ]; then dist/Tahoe-LAFS/tahoe --version; fi
-
-after_success:
-  - if [ "${T}" = "coverage" ]; then codecov; fi
 
 notifications:
   email: false