man: s_server: fix text repetition in -alpn description

Reviewed-by: NTomas Mraz <tomas@openssl.org>
Reviewed-by: NDmitry Belyavskiy <beldmit@gmail.com>
(Merged from https://github.com/openssl/openssl/pull/15099)

doc/man1/openssl-s_server.pod.in

@@ -672,7 +672,7 @@ disabling the ephemeral DH cipher suites.
 
 =item B<-alpn> I<val>, B<-nextprotoneg> I<val>
 
-These flags enable the Enable the Application-Layer Protocol Negotiation
+These flags enable the Application-Layer Protocol Negotiation
 or Next Protocol Negotiation (NPN) extension, respectively. ALPN is the
 IETF standard and replaces NPN.
 The I<val> list is a comma-separated list of supported protocol