Handle automatic macro expansion by elisp-completion-at-point

Handle automatic macro expansion by elisp-completion-at-point

The function `elisp--local-variables' inserts an unbound variable,
`elisp--witness--lisp', into macro forms to determine the locally bound
variables for `elisp-completion-at-point'. It ends up throwing a lot of errors
since it can occupy the position of a keyword (or look like a second argument to
a keyword that takes one). Deleting it when it's at the top level should be
harmless since there should be no locally bound variables to discover here
anyway.