Revert "tests: Add additional self-tests to the AppVeyor suite which exercise Mongo."

This reverts commit 3062995801.

The tests exhibited on AppVeyor showed some very clear failures in the way
that we're killing PIDs on Windows using `taskkill`.  I haven't actually
checked, but I find it virtually impossible that the PID of the process to
kill (the 5th test run) happened to be 3000.

scripts/windows/appveyor/test.ps1

@@ -4,8 +4,6 @@ $jUnit = Join-Path $env:TEMP 'self-test-junit-0.xml'
 $tests = @(
   '^assets'
   '^autoupdate'
-  '^create$'
-  'mongo'
   '^dynamic import.*development'
 ) -Join '|'