[SPARK-14366] Remove sbt-idea plugin

## What changes were proposed in this pull request?

Remove sbt-idea plugin as importing sbt project provides much better support.

Author: Luciano Resende <lresende@apache.org>

Closes #12151 from lresende/SPARK-14366.

project/plugins.sbt

@@ -2,8 +2,6 @@ addSbtPlugin("com.eed3si9n" % "sbt-assembly" % "0.11.2")
 
 addSbtPlugin("com.typesafe.sbteclipse" % "sbteclipse-plugin" % "4.0.0")
 
-addSbtPlugin("com.github.mpeltonen" % "sbt-idea" % "1.6.0")
-
 addSbtPlugin("net.virtual-void" % "sbt-dependency-graph" % "0.8.2")
 
 addSbtPlugin("org.scalastyle" %% "scalastyle-sbt-plugin" % "0.8.0")