Remove unused scala version variables

Author: lolgab

build.sc

@@ -1,10 +1,5 @@
 import mill._, scalalib._, scalajslib._, scalanativelib._, publish._
 
-val scala211 = "2.11.12"
-val scala212 = "2.12.13"
-val scala213 = "2.13.4"
-val scala3 = "3.0.0-M3"
-
 val dottyVersions = sys.props.get("dottyVersion").toList
 
 val scalaVersions = "2.11.12" :: "2.12.13" :: "2.13.4" :: "3.0.0-M3" :: dottyVersions