loader: Downgrade layer json warning to info

The loader used to warn when using the vkGet*ProcAddr fields
in a layer json file from 1.1.0 on. However, it was desirable for
applications to still use this field to allow support from older
loaders. As such, this is no longer a warning.

Change-Id: I401febffe0a15081772dd4a791f5fffbd98d6ac9