[modules] Introduce new VariableLocation for module imports/exports.

src/ast/variables.cc

Index: src/ast/variables.cc
diff --git a/src/ast/variables.cc b/src/ast/variables.cc
index 44f263aa74aeb5c94617e6ffabff596482b8c261..f80822d1a6622ff244253cfbfd8becc5122a2335 100644
--- a/src/ast/variables.cc
+++ b/src/ast/variables.cc
@@ -20,7 +20,6 @@ const char* Variable::Mode2String(VariableMode mode) {
     case CONST_LEGACY: return "CONST_LEGACY";
     case LET: return "LET";
     case CONST: return "CONST";
-    case IMPORT: return "IMPORT";
     case DYNAMIC: return "DYNAMIC";
     case DYNAMIC_GLOBAL: return "DYNAMIC_GLOBAL";
     case DYNAMIC_LOCAL: return "DYNAMIC_LOCAL";