man3: Drop warning about using security levels higher than 1.

man3: Drop warning about using security levels higher than 1.

Today, majority of web-browsers reject communication as allowed by the
security level 1. Instead key sizes and algorithms from security level
2 are required. Thus remove the now obsolete warning against using
security levels higher than 1. For example Ubuntu, compiles OpenSSL
with security level set to 2, and further restricts algorithm versions
available at that security level.

Reviewed-by: Kurt Roeckx <kurt@roeckx.be>
Reviewed-by: Ben Kaduk <kaduk@mit.edu>
(Merged from https://github.com/openssl/openssl/pull/12444)