Remove Java 11 assertion from project settings

This is not necessary. We pass `-release:11` in Scala options so the Scala compiler is already going to enforce that Java 11 is the minimum supported version. Because of this PR: guardian/scala-steward-public-repos#67 running Scala steward for frontend was failing due to this assertion because Scala Steward is running with Java 21.

Co-authored-by: Roberto Tyley <roberto.tyley@gmail.com>

project/ProjectSettings.scala

@@ -33,13 +33,6 @@ object ProjectSettings {
     Compile / doc / sources := Seq.empty,
     Compile / doc := target.map(_ / "none").value,
     scalaVersion := "2.13.13",
-    initialize := {
-      val _ = initialize.value
-      assert(
-        sys.props("java.specification.version") == "11",
-        "Java 11 is required for this project.",
-      )
-    },
     cleanAll := Def.taskDyn {
       val allProjects = ScopeFilter(inAnyProject)
       clean.all(allProjects)