C++: Address review comment

Author: jketema

cpp/ql/lib/semmle/code/cpp/exprs/Expr.qll

@@ -6,7 +6,6 @@ import semmle.code.cpp.Element
 private import semmle.code.cpp.Enclosing
 private import semmle.code.cpp.internal.ResolveClass
 private import semmle.code.cpp.internal.AddressConstantExpression
-private import semmle.code.cpp.internal.ExtractorVersion
 
 /**
  * A C/C++ expression.