Bug 1632354 - Switch a few mach commands to python 3. r=rstewart

Differential Revision: https://phabricator.services.mozilla.com/D72087

mach

@@ -17,17 +17,13 @@ py2commands="
     artifact
     awsy-test
     browsertime
-    buildsymbols
     cargo
     check-spidermonkey
     clang-format
-    compileflags
     cppunittest
     cramtest
     crashtest
     devtools-css-db
-    doctor
-    empty-makefiles
     file-info
     firefox-ui-functional
     geckodriver
@@ -37,17 +33,13 @@ py2commands="
     gtest
     hazards
     ide
-    install
     jsapi-tests
     jsshell-bench
     jstestbrowser
     jstests
     marionette-test
     mochitest
-    mozbuild-reference
     mozharness
-    package
-    package-multi-locale
     pastebin
     power
     prettier-format
@@ -63,9 +55,7 @@ py2commands="
     repackage
     resource-usage
     robocop
-    run
     rusttests
-    show-log
     static-analysis
     talos-test
     taskcluster-build-image
@@ -78,7 +68,6 @@ py2commands="
     try
     valgrind-test
     visualmetrics
-    warnings-list
     web-platform-tests
     web-platform-tests-update
     webidl-example