doc: Remove outdated information about boost versions
doc: Remove outdated information about boost versions

Bitcoin core should work with any remotely recent boost version
if a proper build environment is present. Remove a confusing comment
from the build documentation.

Rebased-From: bd45b1a

Conflicts:
	doc/build-unix.md

langerhans/dogecoin,Exceltior/dogecoin,coinkeeper/2015-06-22_18-37_dogecoin,Domer85/dogecoin,haisee/dogecoin,haisee/dogecoin,haisee/dogecoin,langerhans/dogecoin,brishtiteveja/sherlockcoin,brishtiteveja/sherlockcoin,haisee/dogecoin,Domer85/dogecoin,coinwarp/dogecoin,jarymoth/dogecoin,Exceltior/dogecoin,Exceltior/dogecoin,coinkeeper/2015-06-22_18-37_dogecoin,brishtiteveja/sherlockcoin,jarymoth/dogecoin,coinwarp/dogecoin,koharjidan/dogecoin,coinkeeper/2015-06-22_18-37_dogecoin,Domer85/dogecoin,coinwarp/dogecoin,jarymoth/dogecoin,koharjidan/dogecoin,haisee/dogecoin,coinkeeper/2015-06-22_18-37_dogecoin,marklai9999/Taiwancoin,marklai9999/Taiwancoin,langerhans/dogecoin,brishtiteveja/sherlockcoin,coinkeeper/2015-06-22_18-37_dogecoin,brishtiteveja/sherlockcoin,marklai9999/Taiwancoin,koharjidan/dogecoin,langerhans/dogecoin,coinwarp/dogecoin,jarymoth/dogecoin,langerhans/dogecoin,Exceltior/dogecoin,Exceltior/dogecoin,koharjidan/dogecoin,langerhans/dogecoin,marklai9999/Taiwancoin,koharjidan/dogecoin,coinwarp/dogecoin,Domer85/dogecoin,jarymoth/dogecoin,koharjidan/dogecoin