bug#14197: 24.3.50; remove `kmacro-bind-to-key' prefix arg

[Drew Adams]

`kmacro-bind-to-key' has _ARG as a required argument.  Interactively
it is the numeric prefix argument.

Presumably this is an internal argument, based on the name.
But it is used nowhere in the code, AFAICT - not in
`kmacro-bind-to-key' or in any other code delivered with Emacs.
 
If it is really useless, as it seems, then remove it, including from
`interactive'.  (Or if it is really useful somehow, describe it in the doc
string.)
 
In GNU Emacs 24.3.50.1 (i386-mingw-nt5.1.2600)
 of 2013-04-02 on ODIEONE
Bzr revision: 112212 cyd@gnu.org-20130402033331-sqegwhqh7u1o0ars
Windowing system distributor `Microsoft Corp.', version 5.1.2600
Configured using:
 `configure --with-gcc (4.7) --no-opt --enable-checking --cflags
 -IC:/Devel/emacs/build/include --ldflags -LC:/Devel/emacs/build/lib'