Changes made to accomodate GSA in Google3 w/ Robolectric

dragViewOffset removed from WallpaperPicker as it was causing
a duplicate resource conflict with launcher3 and was not used
within the WallpaperPicker project.

Empty <application> tag added to WallpaperPicker manifest as required by
Robolectric

Removed <add-resource> tag from L3 manifest, unrecognized by Robolectric

Change-Id: I3744fc50731f82c3e6fdc01d9819e9a0302dc503