[flang] remove bogus header include from llvm#164988 (llvm#166906)

I mistakenly added this header in llvm#164988 while I ended-up not using it.
It is causing build failures on some buildbot because of MLIR .inc
dependencies not reflected in cmake.
https://lab.llvm.org/buildbot/#/builders/124/builds/1604
Remove it.

Author: jeanPerier

flang/lib/Optimizer/Builder/HLFIRTools.cpp

@@ -18,7 +18,6 @@
 #include "flang/Optimizer/Builder/Todo.h"
 #include "flang/Optimizer/Dialect/FIRType.h"
 #include "flang/Optimizer/HLFIR/HLFIROps.h"
-#include "flang/Optimizer/OpenMP/Passes.h"
 #include "mlir/IR/IRMapping.h"
 #include "mlir/Support/LLVM.h"
 #include "llvm/ADT/TypeSwitch.h"