[SPARK-5648][SQL] support "alter ... unset tblproperties("key")"

make hivecontext support "alter ... unset tblproperties("key")"
like :
alter view viewName unset tblproperties("k")
alter table tableName unset tblproperties("k")

Author: DoingDone9 <799203320@qq.com>

Closes #4424 from DoingDone9/unset and squashes the following commits:

6dd8bee [DoingDone9] support "alter ... unset tblproperties("key")"