SBT script should not try to set SPARK_HOME
SBT script should not try to set SPARK_HOME

I'm assuming this is left over from the Spark SBT script. We want to set
SPARK_HOME to be a sudirectory of the project dir (not the root);
it's now set in the run Python script.

mengxr/spark-perf,nchammas/spark-perf,databricks/spark-perf,zsxwing/spark-perf,jkbradley/spark-perf,feynmanliang/spark-perf,arijitt/spark-perf,feynmanliang/spark-perf,Altiscale/spark-perf,databricks/spark-perf,zsxwing/spark-perf,mengxr/spark-perf,Altiscale/spark-perf,XiaoqingWang/spark-perf,arijitt/spark-perf,XiaoqingWang/spark-perf,jkbradley/spark-perf,nchammas/spark-perf