Make WithoutPreciseParameterTypes mandatory

No need to make it optional, since we will defer to 3.1 anyway.

Author: odersky

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

@@ -760,7 +760,7 @@ class Definitions {
   @tu lazy val LanguageDeprecatedModule: Symbol = requiredModule("scala.language.deprecated")
   @tu lazy val NonLocalReturnControlClass: ClassSymbol = requiredClass("scala.runtime.NonLocalReturnControl")
   @tu lazy val SelectableClass: ClassSymbol = requiredClass("scala.Selectable")
-  @tu lazy val WithoutPreciseParameterTypesClass: Symbol = getClassIfDefined("scala.Selectable.WithoutPreciseParameterTypes")
+  @tu lazy val WithoutPreciseParameterTypesClass: Symbol = requiredClass("scala.Selectable.WithoutPreciseParameterTypes")
           // todo: make this a required class from 3.1 on
 
   @tu lazy val ReflectPackageClass: Symbol = requiredPackage("scala.reflect.package").moduleClass