Reduce the number of images to test on AppVeyor, to speed up the build

Author: SRombauts

appveyor.yml

@@ -7,10 +7,11 @@ version: "{build}"
 install:
   - git submodule update --init --recursive
 
-image:
+image:
+# Reduce the number of images to test on AppVeyor, to speed up the build
   - Visual Studio 2022
-  - Visual Studio 2019
-  - Visual Studio 2017
+#  - Visual Studio 2019
+#  - Visual Studio 2017
   - Visual Studio 2015
 
 # configurations to add to build matrix