Remove placeholder check from DeclaredName linter

The `CapitalizationInSelector` linter now checks for improper
capitalization for placeholder selectors. Thus we can remove the
placeholder-related checks from the `DeclardName` linter (or else we'll
get double-reporting on the error).

Change-Id: If964bcc8cbc1b98f192c04d35c435c9ebe64c8be
Reviewed-on: https://gerrit.causes.com/28831
Tested-by: jenkins <jenkins@causes.com>
Reviewed-by: Greg Hurrell <greg@causes.com>