Appveyor: Don't try to install the mingw openssl package

This package conflicts with a preinstalled mingw openssl.

Fixes bug 27943. I think this was an appveyor change, not a Tor bug.

.appveyor.yml

@@ -30,7 +30,7 @@ install:
     {
         Execute-Command 'c:\msys64\usr\bin\bash' '-e' '-c' $args
     }
-    Execute-Command "C:\msys64\usr\bin\pacman" -Sy --needed --noconfirm openssl-devel openssl libevent-devel libevent ${env:mingw_prefix}-libevent ${env:mingw_prefix}-openssl ${env:mingw_prefix}-zstd
+    Execute-Command "C:\msys64\usr\bin\pacman" -Sy --needed --noconfirm openssl-devel openssl libevent-devel libevent ${env:mingw_prefix}-libevent ${env:mingw_prefix}-zstd ;
 
 build_script:
 - ps: >-