.gitignore: Fix Windows-related .gitignore

packaging/.gitignore has an entry starting with /packaging/windows
unlike the one just before it which is just /windows. This looks like an
oversight. This commit removes it.

Author: cfergeau

packaging/.gitignore

@@ -7,7 +7,7 @@ root/
 /VERSION
 /ARCH
 /windows/msi/
-packaging/windows/product.wxs
+/windows/product.wxs
 vfkit.entitlements
 /tmp
 /*.pkg