libkmod: remove internal kmod_list iterators

libkmod: remove internal kmod_list iterators

These were introduced to workaround since the compiler cannot properly
optimise things, since the symbols have external linkage.

These days this is not so much an issue. For example comparing a gcc 14
build, with -O2 shows 24 bytes growth with this reverted.

Although in practise anyone looking for extreme optimisations - be that
speed or size - should be using LTO and/or PGO.

Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com>
Link: https://github.com/kmod-project/kmod/pull/117
Signed-off-by: Lucas De Marchi <lucas.de.marchi@gmail.com>