libstatgrab: only use one configure test for 0.90 API change

Previously, each API change was tested in configure.ac. Some of the
tests are relying on signature checks and would need to have -Werror
flag enabled to make them work. This is quite fragile.

Instead, we assume that if `sg_init()` requires an argument, we must use
the 0.90 API.

Fixes: #795 

This is one possible fix for the problem introduced in c963d35fb88b7db81fcf6e3db51313d9002e17b4