doc: Remove outdated information about boost versions
doc: Remove outdated information about boost versions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

domob1812/crowncoin,Crowndev/crowncoin,Crowndev/crowncoin,Crowndev/crowncoin,Infernoman/crowncoin,Infernoman/crowncoin,Crowndev/crowncoin,domob1812/crowncoin,syscoin/syscoin,syscoin/syscoin,domob1812/crowncoin,Crowndev/crowncoin,Infernoman/crowncoin,syscoin/syscoin,Crowndev/crowncoin,Infernoman/crowncoin,Infernoman/crowncoin,syscoin/syscoin,domob1812/crowncoin,syscoin/syscoin,domob1812/crowncoin,syscoin/syscoin,syscoin/syscoin,Infernoman/crowncoin,syscoin/syscoin,domob1812/crowncoin