boost: bump to 1.65.1, coroutine2 is now a header only library

boost: bump to 1.65.1, coroutine2 is now a header only library

The coroutine2 functionality is now provided only through headers, the
compiled library has disappeared. Due to that passing "coroutine2" as
argument to --without-libraries. Hence, the
BR2_PACKAGE_BOOST_COROUTINE2 option is removed by this commit.

We don't need Config.in.legacy handling, because coroutine2 support is
now unconditionally available in boost.

While at it, add LICENSE_1_0.txt sha256sum to boost.hash.

Signed-off-by: Adam Duskett <Adamduskett@outlook.com>
[Thomas: drop Config.in.legacy handling, reword commit log.]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>