move unused-import check to sbt only

pom.xml

@@ -164,7 +164,6 @@
     <commons.collections.version>3.2.2</commons.collections.version>
     <scala.version>2.12.10</scala.version>
     <scala.binary.version>2.12</scala.binary.version>
-    <scalac.arg.unused-imports>-Ywarn-unused-import</scalac.arg.unused-imports>
     <scalatest-maven-plugin.version>2.0.0</scalatest-maven-plugin.version>
     <scalafmt.parameters>--test</scalafmt.parameters>
     <!-- for now, not running scalafmt as part of default verify pipeline -->
@@ -2538,7 +2537,6 @@
               <arg>-deprecation</arg>
               <arg>-feature</arg>
               <arg>-explaintypes</arg>
-              <arg>${scalac.arg.unused-imports}</arg>
               <arg>-target:jvm-1.8</arg>
             </args>
             <jvmArgs>
@@ -3262,13 +3260,12 @@
         </pluginManagement>
       </build>
     </profile>
-    
+
     <profile>
       <id>scala-2.13</id>
       <properties>
         <scala.version>2.13.3</scala.version>
         <scala.binary.version>2.13</scala.binary.version>
-        <scalac.arg.unused-imports>-Wconf:cat=unused-imports:e</scalac.arg.unused-imports>
       </properties>
       <dependencyManagement>
         <dependencies>

project/SparkBuild.scala

@@ -221,6 +221,7 @@ object SparkBuild extends PomBuild {
         Seq(
           "-Xfatal-warnings",
           "-deprecation",
+          "Ywarn-unused-import",
           "-P:silencer:globalFilters=.*deprecated.*" //regex to catch deprecation warnings and supress them
         )
       } else {
@@ -230,6 +231,7 @@ object SparkBuild extends PomBuild {
           // see `scalac -Wconf:help` for details
           "-Wconf:cat=deprecation:wv,any:e",
           // 2.13-specific warning hits to be muted (as narrowly as possible) and addressed separately
+          "-Wconf:cat=unused-imports:e",
           "-Wconf:cat=lint-multiarg-infix:wv",
           "-Wconf:cat=other-nullary-override:wv",
           "-Wconf:cat=other-match-analysis&site=org.apache.spark.sql.catalyst.catalog.SessionCatalog.lookupFunction.catalogFunction:wv",