Drop legacy prime-generation callback in setup_certificate (#48)

The `BN_GENCB` block only printed progress dots in verbose mode, but it
re-enters Ruby from inside OpenSSL's keygen.

Under ZJIT that re-entry intermittently aborts generation with
`EVP_PKEY_keygen`. The callback form is obsolete in OpenSSL 3.x, so just
generate the key without it.

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

Author: hsbt

lib/drb/ssl.rb

@@ -170,19 +170,7 @@ def setup_certificate
           return
         end
 
-        rsa = OpenSSL::PKey::RSA.new(2048){|p, n|
-          next unless self[:verbose]
-          case p
-          when 0; $stderr.putc "."  # BN_generate_prime
-          when 1; $stderr.putc "+"  # BN_generate_prime
-          when 2; $stderr.putc "*"  # searching good prime,
-                                    # n = #of try,
-                                    # but also data from BN_generate_prime
-          when 3; $stderr.putc "\n" # found good prime, n==0 - p, n==1 - q,
-                                    # but also data from BN_generate_prime
-          else;   $stderr.putc "*"  # BN_generate_prime
-          end
-        }
+        rsa = OpenSSL::PKey::RSA.new(2048)
 
         cert = OpenSSL::X509::Certificate.new
         cert.version = 2 # This means v3