Remove restriction that @functionBuilders have to be uppercased;

we're not doing this anymore.

Author: rjmccall

include/swift/AST/DiagnosticsSema.def

@@ -4478,8 +4478,6 @@ ERROR(function_builder_control_flow, none,
 NOTE(note_function_builder_control_flow, none,
       "closure containing control flow statement cannot be used with function "
       "builder %0", (DeclName))
-ERROR(function_builder_reserved_name, none,
-      "function builder type name must start with an uppercase letter", ())
 ERROR(function_builder_attribute_not_allowed_here, none,
       "function builder attribute %0 can only be applied to a parameter, "
       "function, or computed property", (DeclName))

lib/Sema/TypeCheckAttr.cpp

@@ -2635,15 +2635,6 @@ void AttributeChecker::visitPropertyWrapperAttr(PropertyWrapperAttr *attr) {
 }
 
 void AttributeChecker::visitFunctionBuilderAttr(FunctionBuilderAttr *attr) {
-  auto nominal = dyn_cast<NominalTypeDecl>(D);
-  if (!nominal)
-    return;
-
-  // Make sure the name isn't reserved.
-  if (isReservedAttributeName(nominal->getName().str())) {
-    nominal->diagnose(diag::function_builder_reserved_name);
-  }
-
   // TODO: check that the type at least provides a `sequence` factory?
   // Any other validation?
 }