debian: fix teflon library path

What does this MR do and why?

debian: fix teflon library path

In 6cfc1774ef, to work around something else broken, the libteflon.so
installation path was overridden to be /usr/lib/libteflon.so. On Debian
arm64, the only architecture where we build teflon on, that is not the
correct library path however.

Debian uses /usr/lib/aarch64-linux-gnu/ as its library path on arm64, in
case users wish to share their same /usr (or non-/usr, since usrmerge is
a matter of taste after all, except when it isn't, cue trout slap fight)
between machines of different architectures, underlying kernels, and C
libraries.

Whatever problem this override once tried to solve, it no longer exists,
so should not be applied anymore. The install path that's chosen by
default is correct, so let's follow what the other libraries do here.

Signed-off-by: Nicolas Frattaroli <nicolas.frattaroli@collabora.com>