C++: Remove outdated comment.

Author: MathiasVP

cpp/ql/lib/semmle/code/cpp/ir/dataflow/internal/DataFlowUtil.qll

@@ -3,9 +3,6 @@
  */
 
 private import cpp
-// The `ValueNumbering` library has to be imported right after `cpp` to ensure
-// that the cached IR gets the same checksum here as it does in queries that use
-// `ValueNumbering` without `DataFlow`.
 private import semmle.code.cpp.ir.ValueNumbering
 private import semmle.code.cpp.ir.IR
 private import semmle.code.cpp.controlflow.IRGuards