remove new over-assertive assert

I added an assert that prevents ExprType to be "trivial types" (i32, f32, ...)
but that actually breaks existing lowering code that generate as_expr + associate
patterns to create temporaries:

https://github.com/llvm/llvm-project/blob/03b5f8f0f0d10c412842ed04b90e2217cf071218/flang/lib/Lower/ConvertCall.cpp#L1271

```
subroutine trivial_as_expr(i)
  integer, optional :: i
  interface
    subroutine foo(j)
      integer, optional, value :: j
    end subroutine
  end interface
  call foo(i)
end subroutine
```

This is unrelated to this patch, so leave it like this (it is not even a
functional problem).

Author: jeanPerier

flang/lib/Optimizer/HLFIR/IR/HLFIRDialect.cpp

@@ -220,8 +220,6 @@ mlir::Type hlfir::getExprType(mlir::Type variableType) {
   hlfir::ExprType::Shape typeShape;
   bool isPolymorphic = fir::isPolymorphicType(variableType);
   mlir::Type type = getFortranElementOrSequenceType(variableType);
-  assert(!fir::isa_trivial(type) &&
-         "numerical and logical scalar should not be wrapped in hlfir.expr");
   if (auto seqType = mlir::dyn_cast<fir::SequenceType>(type)) {
     assert(!seqType.hasUnknownShape() && "assumed-rank cannot be expressions");
     typeShape.append(seqType.getShape().begin(), seqType.getShape().end());