Refactor -engine documentation

Common wording courtesy Richard Levitte.

Reviewed-by: Dmitry Belyavskiy <beldmit@gmail.com>
Reviewed-by: Tomas Mraz <tmraz@fedoraproject.org>
(Merged from https://github.com/openssl/openssl/pull/10128)
diff --git a/doc/man1/openssl-genrsa.pod.in b/doc/man1/openssl-genrsa.pod.in
index 16b887b..8a815ee 100644
--- a/doc/man1/openssl-genrsa.pod.in
+++ b/doc/man1/openssl-genrsa.pod.in
@@ -24,10 +24,10 @@
 [B<-des3>]
 [B<-idea>]
 [B<-f4>|B<-3>]
-[B<-engine> I<id>]
 [B<-primes> I<num>]
 [B<-verbose>]
 {- $OpenSSL::safe::opt_r_synopsis -}
+{- $OpenSSL::safe::opt_engine_synopsis -}
 [B<numbits>]
 
 =for openssl ifdef engine
@@ -65,13 +65,6 @@
 
 The public exponent to use, either 65537 or 3. The default is 65537.
 
-=item B<-engine> I<id>
-
-Specifying an engine (by its unique I<id> string) will cause this command
-to attempt to obtain a functional reference to the specified engine,
-thus initialising it if needed. The engine will then be set as the default
-for all available algorithms.
-
 =item B<-primes> I<num>
 
 Specify the number of primes to use while generating the RSA key. The I<num>
@@ -85,6 +78,8 @@
 
 {- $OpenSSL::safe::opt_r_item -}
 
+{- $OpenSSL::safe::opt_engine_item -}
+
 =item B<numbits>
 
 The size of the private key to generate in bits. This must be the last option