compiletest: autoremove duplicate .nll.* files (#51204)
compiletest: autoremove duplicate .nll.* files (#51204)

UI tests in bless mode should now check to see if `.nll.*` files have a
matching `.*` file. If a match is found, it will be deleted.
This should be extensible to other modes (i.e., Polonius).
On running with `--bless`, the two files removed in #51186 are, in turn,
removed automatically.

GBGamer/rust,GBGamer/rust,GBGamer/rust,graydon/rust,aidancully/rust,GBGamer/rust,graydon/rust,aidancully/rust,aidancully/rust,aidancully/rust,GBGamer/rust,graydon/rust,graydon/rust,GBGamer/rust,aidancully/rust,aidancully/rust,GBGamer/rust,graydon/rust,graydon/rust,GBGamer/rust