Remove sbt-fix-it module

[alejandrohdezma]

Removing this plugin since it's only useful for projects using both tools that also use the IntegrationTest configuration.

The same goal can be met by adding the following AutoPlugin to your project folder:

object IntegrationTestPlugin extends AutoPlugin {

  override def trigger               = allRequirements
  override def requires              = ScalafmtPlugin && ScalafixPlugin
  override def projectConfigurations = Seq(IntegrationTest)

  override def projectSettings = inConfig(IntegrationTest) {
    testSettings ++ scalafixConfigSettings(IntegrationTest) ++ scalafmtConfigSettings
  }

}