remove duplicate warning

Though perhaps, the emphasis is warranted given its importance. :-)

bip-schnorr.mediawiki

@@ -161,9 +161,6 @@ To sign ''m'' for public key ''dG'':
 '''Above deterministic derivation of ''R'' is designed specifically for this signing algorithm and may not be secure when used in other signature schemes.'''
 For example, using the same derivation in the MuSig multi-signature scheme leaks the secret key (see the [https://eprint.iacr.org/2018/068 MuSig paper] for details).
 
-'''Above deterministic derivation of ''R'' is designed specifically for this signing algorithm and may not be secure when used in other signature schemes.'''
-For example, using the same derivation in the MuSig multi-signature scheme leaks the secret key (see the [https://eprint.iacr.org/2018/068 MuSig paper] for details).
-
 Note that this is not a ''unique signature'' scheme: while this algorithm will always produce the same signature for a given message and public key, ''k'' (and hence ''R'') may be generated in other ways (such as by a CSPRNG) producing a different, but still valid, signature.
 
 === Optimizations ===