bmx6: drop package

bmx6: drop package

This package is no longer maintained by us or by upstream developers.
The last version in the GitHub repository is from 2020 with no activity so far.
We are using version 0.1-alpha.

Because LuCI app is vulnerable to several CVEs and DependencyBot still
sends emails about it, let's drop it.

If anyone wants, they can use bmx7.

Signed-off-by: Josef Schlehofer <[email protected]>
(cherry picked from commit 9fb9d9343ea27d6dbb5008ece10c0c843dd2c781)