please revert "Add replacement hack for Android's broken ttyname."

[Hans-Christoph Steiner]

So the first attempt at the ttyname workaround causes build issues
because first, adding "#undef HAVE_TTYNAME" to config.h just gets
rewritten to "#define HAVE_TTYNAME 1" later on in the build process.
When HAVE_TTYNAME is actually undefined, then the gnupg code uses the
Windows ttyname() stub which just returns a 0, but then that conflicts
with then Android ttyname() stub, which also just returns a 0.

So if a stub ttyname() returning a 0 is all that gnupg needs, Android
already provides that, albeit with the "FIXME warning message".

.hc