dropbear: disable two weak kex/mac algorithms

dropbear: disable two weak kex/mac algorithms

hmac-sha1 and diffie-hellman-group14-sha1 are weak algorithms.
A future deprecation notice of ssh-rsa (2048-bit) has been issued. [1]

It has no place in a potentially internet-facing daemon like dropbear.
Upstream has acknowledged this and offered this solution to disable
these two until this is made to be the default in the next release
of dropbear next year. [2]

1. https://www.openssh.com/txt/release-8.2
2. https://github.com/mkj/dropbear/issues/138

Signed-off-by: John Audia <therealgraysky@proton.me>
Signed-off-by: Konstantin Demin <rockdrilla@gmail.com>