docs: improve pluginAPI docs

setFileAttributes() is implemented and can be used, so don't document it
isn't.

docs/manuals/source/DeveloperGuide/pluginAPI.rst

@@ -740,7 +740,7 @@ time values for the directory entry.
 setFileAttributes(bpContext \*ctx, struct restore_pkt \*rp)
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
-This is call not yet implemented. Called for a command plugin.
+Called for a command plugin.
 
 See the definition of **restore_pkt** in the above section.