remove Appveyor's Vs2010 and 13 builds (#6969)

diff --git a/appveyor.yml b/appveyor.yml
index 3876b16..fdbe9e5 100644
--- a/appveyor.yml
+++ b/appveyor.yml
@@ -15,16 +15,6 @@
 
   matrix:
     - APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2015
-      CMAKE_VS_VERSION: "10 2010"
-      CMAKE_OPTIONS: "-DFLATBUFFERS_BUILD_LEGACY=1 -DFLATBUFFERS_SKIP_MONSTER_EXTRA=ON"
-      CHECK_GEN_CODE: 0
-
-    - APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2015
-      CMAKE_VS_VERSION: "12 2013"
-      CMAKE_OPTIONS: "-DFLATBUFFERS_SKIP_MONSTER_EXTRA=ON"
-      CPP_TEST_OPTIONS: "--skip-monster-extra"
-
-    - APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2015
       CMAKE_VS_VERSION: "14 2015"
 
 platform: