Revert "Build.scala: hardcode maximum number of parallel tasks to 8"

This reverts commit 214bb04.

Author: smarter

project/Build.scala

@@ -54,9 +54,6 @@ object DottyBuild extends Build {
 
   override def settings: Seq[Setting[_]] = {
     super.settings ++ Seq(
-      concurrentRestrictions in Global := {
-        Tags.limitAll(8) :: Nil
-      },
       scalaVersion in Global := scalacVersion,
       version in Global := dottyVersion,
       organization in Global := dottyOrganization,