rm ‘public static final’ modifiers from field declarations within interfaces

Change-Id: I2154052f89787b6fe17edb2f6e6ea132347b3d13
Reviewed-on: https://gerrit.libreoffice.org/11971
Reviewed-by: Noel Grandin <noelgrandin@gmail.com>
Tested-by: Noel Grandin <noelgrandin@gmail.com>