No longer specify version of lowest supported toolchain in README
No longer specify version of lowest supported toolchain in README

It's tedious having to update it every time it changes, and we no longer
have any Travis tasks that need updating.

Note that we missed a few updates of the README, probably because that's
all there is to do in this repo anymore.

Signed-off-by: mulhern <7b51bcf507bcd7afb72bf8663752c0ddbeb517f6@redhat.com>

stratis-storage/stratisd,stratis-storage/stratisd,stratis-storage/stratisd