jenkins: Don't fetch --prune unnecessarily, print build version on Windows

jenkins/build-windows.bat

@@ -24,6 +24,7 @@ cd src\github.com\syncthing\syncthing
 echo Initializing ^& cleaning
 go version
 git clean -fxd || goto error
+go run build.go version
 echo.
 
 echo Fetching extras

jenkins/common.bash

@@ -32,7 +32,6 @@ function clean {
     echo Cleaning
     rm -rf "$GOPATH/pkg"
     git clean -fxd
-    git fetch --prune
     echo
 }