tcpdump.1.in: Delete Linux 2.0 references

Delete Linux 2.0 bugs from bug list.

Linux 2.0.x releases are from 1996-2004. The man page recommended upgrading to Linux 2.2, released in 1999.

https://en.wikipedia.org/wiki/Linux_kernel_version_history#Releases_up_to_2.6.0

I'm assuming these >20 year old bug references aren't that useful now.