openssl enc: Don't unbuffer stdin

- unbuffer causes single-byte reads from stdin and poor performance

Fixes #3281
CLA: trivial

Reviewed-by: Rich Salz <rsalz@openssl.org>
Reviewed-by: Richard Levitte <levitte@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/3299)

apps/enc.c

@@ -291,7 +291,6 @@ int enc_main(int argc, char **argv)
     buff = app_malloc(EVP_ENCODE_LENGTH(bsize), "evp buffer");
 
     if (infile == NULL) {
-        unbuffer(stdin);
         in = dup_bio_in(informat);
     } else
         in = bio_open_default(infile, 'r', informat);