selftests: net: tls: remove recv_rcvbuf test

selftests: net: tls: remove recv_rcvbuf test

This test only works when [1] is applied, which was rejected.

Basically, the errors are reported and cleared. In this particular case of
tls sockets, following reads will block.

The test case was originally submitted with the rejected patch, but, then,
was included as part of a different patchset, possibly by mistake.

[1] https://lore.kernel.org/netdev/20191007035323.4360-2-jakub.kicinski@netronome.com/#t

Thanks Paolo Pisati for pointing out the original patchset where this
appeared.

Fixes: 65190f77424d (selftests/tls: add a test for fragmented messages)
Reported-by: Paolo Pisati <paolo.pisati@canonical.com>
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>