Drop Configuration.clone()

There was no reason not to use the original configuration.

Author: nex3

lib/src/configuration.dart

@@ -69,9 +69,4 @@ class Configuration {
     }
     return Configuration(newValues, isImplicit: isImplicit);
   }
-
-  /// Creates a copy of this configuration.
-  Configuration clone() => isEmpty
-      ? const Configuration.empty()
-      : Configuration({...values}, isImplicit: isImplicit);
 }

lib/src/visitor/async_evaluate.dart

@@ -630,7 +630,7 @@ class _EvaluateVisitor
       _atRootExcludingStyleRule = false;
       _inKeyframes = false;
 
-      if (configuration != null) _configuration = configuration.clone();
+      if (configuration != null) _configuration = configuration;
 
       await visitStylesheet(stylesheet);
       css = _outOfOrderImports == null

lib/src/visitor/evaluate.dart

@@ -5,7 +5,7 @@
 // DO NOT EDIT. This file was generated from async_evaluate.dart.
 // See tool/grind/synchronize.dart for details.
 //
-// Checksum: 63ce60ba47ac04b49e0a3edbe9038fb13b037e64
+// Checksum: de58af7bb88d7a688632ff096930a5d2be263a6d
 //
 // ignore_for_file: unused_import
 
@@ -634,7 +634,7 @@ class _EvaluateVisitor
       _atRootExcludingStyleRule = false;
       _inKeyframes = false;
 
-      if (configuration != null) _configuration = configuration.clone();
+      if (configuration != null) _configuration = configuration;
 
       visitStylesheet(stylesheet);
       css = _outOfOrderImports == null