Please remove wrapping of functions deprecated in GSL 2.2.1

[rbalint]

GSL deprecated a few functions which may not be available on all platforms.
GSL in Debian for example disabled deprecated functions in the official package in unstable resulting build failure in rb-gsl: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=841611

[v0dro]

Whoa. Alright. Thanks.

[rbalint]

Having a new release without tho deprecated functions would be nice in the next weeks to let Debian package a working rb-gsl in the next stable release.

[rbalint]

For the record Dirk, the GLS maintainer has enabled the deprecated functions in Debian which allows rb-gsl to build now, but disabling the deprecated functions in rb-gsl would be welcome anyway.