AppVeyor: remove Python 3.5

Build failed with:
rc.exe -Isrc -IC:\Python35-x64\include -IC:\Python35-x64\include "-IC:\Program Files (x86)\Microsoft Visual Studio 14.0\VC\INCLUDE" "-IC:\Program Files (x86)\Microsoft Visual Studio 14.0\VC\ATLMFC\INCLUDE" "-IC:\Program Files (x86)\Windows Kits\10\include\10.0.22000.0\ucrt" "-IC:\Program Files (x86)\Windows Kits\NETFXSDK\4.6.1\include\um" "-IC:\Program Files (x86)\Windows Kits\10\include\10.0.22000.0\shared" "-IC:\Program Files (x86)\Windows Kits\10\include\10.0.22000.0\um" "-IC:\Program Files (x86)\Windows Kits\10\include\10.0.22000.0\winrt" /fobuild\temp.win-amd64-3.5\Release\pykcs11.res pykcs11.rc
error: command 'rc.exe' failed: No such file or directory
Command exited with code 1

appveyor.yml

@@ -12,7 +12,6 @@ environment:
     - PYTHON: "C:\\Python37-x64"
     - PYTHON: "C:\\Python36"
     - PYTHON: "C:\\Python36-x64"
-    - PYTHON: "C:\\Python35-x64"
 
 cache:
   ## Cache swig, which we install via AppVeyor.