Remove zte device tree builds
    
    The zte vendor directory has been dropped in 5.12.rc1 via this change:
    
      commit 89d4f98ae90d95716009bb89823118a8cfbb94dd
      Author: Arnd Bergmann <arnd@arndb.de>
      Date:   Mon Jan 18 14:06:09 2021 +0100
    
    Signed-off-by: Matthias Brugger <mbrugger@suse.com>