bip-0174: remove duplicated 'only' (typo)

Author: darosior

bip-0174.mediawiki

@@ -313,7 +313,7 @@ If a Signer cannot sign a transaction, it must not add a Partial Signature.
 
 The Signer can additionally compute the addresses and values being sent, and the transaction fee,  optionally showing this data to the user as a confirmation of intent and the consequences of signing the PSBT.
 
-Signers do not need to sign for all possible input types. For example, a signer may choose to only sign only Segwit inputs.
+Signers do not need to sign for all possible input types. For example, a signer may choose to only sign Segwit inputs.
 
 A single entity is likely to be both a Signer and an Updater as it can update a PSBT with necessary information prior to signing it.