package/opentyrian: switch to using github

package/opentyrian: switch to using github

OpenTyrian was previously managed in a Mercurial repository hosted on
Bitbucket. Mid-2020, Bitbucket shut off all its Mercurial repositories:
    https://bitbucket.org/blog/sunsetting-mercurial-support-in-bitbucket

Since then, OpenTyrian's source code is inacessible, but we have had no
build failure associated as there is an old archive hosted on s.b.o, so
that all builds fallback to downloading that:
    http://sources.buildroot.net/opentyrian/opentyrian-9c9f0ec3532b.tar.gz

However, the project has been revived (kinda) on github:
    https://github.com/opentyrian/opentyrian

Git commit cf5dbeb69eebd9ef9afc4473088d9469b79589eb has been found to
be the closest, both in content and date, to the Mercuail reference
9c9f0ec3532b we were using. The only deltas are in Mercurial-specific
files:

 b/.hg_archival.txt |    5     0     5     0 -----
 b/.hgtags          |    2     1     1     0 +-
 2 files changed, 1 insertion(+), 6 deletions(-)

While at it, add a hash file.

Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>
Cc: Julien Boibessot <julien.boibessot@armadeus.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>