Remove check for declare modifier on interface

Author: Yui T

src/compiler/checker.ts

@@ -12361,9 +12361,6 @@ module ts {
  else if ((node.kind === SyntaxKind.ImportDeclaration || node.kind === SyntaxKind.ImportEqualsDeclaration) && flags & NodeFlags.Ambient) {
  return grammarErrorOnNode(lastDeclare, Diagnostics.A_declare_modifier_cannot_be_used_with_an_import_declaration, "declare");
  }
- else if (node.kind === SyntaxKind.InterfaceDeclaration && flags & NodeFlags.Ambient) {
- return grammarErrorOnNode(lastDeclare, Diagnostics.A_declare_modifier_cannot_be_used_with_an_interface_declaration, "declare");
- }
  else if (node.kind === SyntaxKind.Parameter && (flags & NodeFlags.AccessibilityModifier) && isBindingPattern((<ParameterDeclaration>node).name)) {
  return grammarErrorOnNode(node, Diagnostics.A_parameter_property_may_not_be_a_binding_pattern);
  }