The message for commit d205e6b clearly states:

--nxagent --clipboard: use clipboardrc instead of builtin clipboard

which indeed describes what happens in this commit.
However, both message and code fail at explaining why such a change is necessary or relevant. Could you please clarify?

Context: on multiple occasions, I found myself unable to copy/paste to/from the applications run through x11docker. My investigations are not complete yet (mainly because this usually happens right when I have other priorities), but I was surprised to notice that nxagent's seemingly interesting clipboard capabilities had been recently replaced with the clipboardrc mechanism.