thirdparty: remove memkind from LICENSE.txt
thirdparty: remove memkind from LICENSE.txt

I'm getting kinda overwhelmed by the sheer number of license files we seem
to be juggling. I guess that's how we missed this one.

Change-Id: I7989fca644f573e90304af4cbf5dc2440fe37d3e
Reviewed-on: http://gerrit.cloudera.org:8080/14703
Tested-by: Kudu Jenkins
Reviewed-by: Alexey Serbin <864f6b82bd94e8dda64141d4274519ee66e0102e@cloudera.com>

helifu/kudu,helifu/kudu,helifu/kudu,helifu/kudu,helifu/kudu,helifu/kudu,helifu/kudu,helifu/kudu,helifu/kudu