Apache on Ubuntu: module dav_module is already loaded
Your vitual host config is fine and has nothing to do with the warning. The problem is created by two included config files both loading mod_dav.so:
mods-enabled/dav_svn.load: loads the DAV module as a dependencymods-enabled/dav.load: (obviously)
dav_svn.load is careful about it and only includes dav.load if the module isn't already loaded, but dav.load has no such check. This works fine if dav.load is included before dav_svn.load, but apparently that doesn't happen in your case (same here, by the way).
I was able to get rid of the warning by changing the content of dav.load from
LoadModule dav_module /usr/lib/apache2/modules/mod_dav.soto
<IfModule !mod_dav.c> LoadModule dav_module /usr/lib/apache2/modules/mod_dav.so</IfModule>