moveonly: Move (Un)Serialize(To/From)Vector, (De)SerializeHDKeypaths to psbt module

SerializeToVector, UnserializeFromVector, DeserializeHDKeypaths, and SerializeHDKeypaths
were in sign.h where PSBT was originally implemented. Since all of the PSBT serialization
has moved to its own file, these functions should follow.

src/test/fuzz/script_sign.cpp

@@ -5,6 +5,7 @@
 #include <chainparams.h>
 #include <chainparamsbase.h>
 #include <key.h>
+#include <psbt.h>
 #include <pubkey.h>
 #include <script/keyorigin.h>
 #include <script/sign.h>