[SPARK-2742][yarn] delete useless variables

Author: XuTingjun <1039320815@qq.com>

Closes #1614 from XuTingjun/yarn-bug and squashes the following commits:

f07096e [XuTingjun] Update ClientArguments.scala
add 'Last' component
fix the bug in 'Last' component
add abs() function support
add abs() function support
add math 'power' function
handle the  non-numeric string