Wood in old Victorian brick wall how do I fill before installing damp course.

[dragonsrest]

Hi I am stripping back a walk in my house before installing dry rods and I found a random piece of wood it is a bit rotten and does not seem to have any function.
What do I do do I treat the wood then fill with mortar grateful for any help also will I need to put additional dryrods and run the damp course over the wood rather than under ?

 

[blup]

A floor joist cut off at wall level, with the remaining piece left in the wall pocket. If so remove and fill with mortar