iproute2: stop writing unused snapshot information

iproute2: stop writing unused snapshot information

iproute2 already generates and uses a proper version string based off
of git since 2020 [1]. Since the aforementioned commit has already
removed the include for SNAPSHOT.h, this bit of code has had no effect
since then other than disabling the built-in configure script invocation.

[1]: https://git.kernel.org/pub/scm/network/iproute2/iproute2.git/commit/?id=fbef655568ee931a82ad463a6f46f01ce3fb27aa

Signed-off-by: George Tsiamasiotis <[email protected]>
Link: https://github.com/openwrt/openwrt/pull/20281
Signed-off-by: Robert Marko <[email protected]>