Drop special case skipping singletons in TypeComparer

Author: odersky

compiler/src/dotty/tools/dotc/core/TypeComparer.scala

@@ -573,12 +573,6 @@ class TypeComparer(initctx: Context) extends ConstraintHandling[AbsentContext] {
         }
         compareTypeLambda
       case OrType(tp21, tp22) =>
-        val tp1a = tp1.widenDealiasKeepRefiningAnnots
-        if (tp1a ne tp1)
-          // Follow the alias; this might avoid truncating the search space in the either below
-          // Note that it's safe to widen here because singleton types cannot be part of `|`.
-          return recur(tp1a, tp2)
-
         // Rewrite T1 <: (T211 & T212) | T22 to T1 <: (T211 | T22) and T1 <: (T212 | T22)
         // and analogously for T1 <: T21 | (T221 & T222)
         // `|' types to the right of <: are problematic, because