pkg-autotools: fold the libtool patching code directly into the hook

We now have only one caller of the libtool patching code, which is the
hook itself.

So, there is no longer any need to extract this code into a utility
function, and it can be folded into the hook itself.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Cc: Arnout Vandecappelle <arnout@mind.be>
Cc: Johan Oudinet <johan.oudinet@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>