Delete spurious branches from Apache

[Boaz Ben-Zvi]

   I mistakenly pushed a branch (“MERGE-180521-01”) into the Apache repo, and 
plan to delete it soon 
(i.e. do  “git push https://github.com/apache/drill.git --delete 
MERGE-180521-01” ).

  Just in case someone notices ....

  On this occasion: Looks like there are other similar such branches:  
“DRILL-3478” and “DRILL-4235” ; any objection to deleting those as well ?

    Thanks,

        Boaz