Remove exported Version func from wallet package.
Remove exported Version func from wallet package.

This function was not implemented (returning zero values) and all
versioning is handled internally by the wallet's ReadFrom and WriteTo
functions.  If the read wallet does not match the latest file version,
it is read in the old format, but always written back with the new
format.

btcsuite/btcwallet,Roasbeef/btcwallet,jrick/btcwallet,synrg-labs/btcwallet,Stash-Crypto/btcwallet,jrick/dcrwallet,Roasbeef/btcwallet,decred/dcrwallet,jrick/btcwallet,btcsuite/btcwallet,Stash-Crypto/btcwallet,synrg-labs/btcwallet,jrick/dcrwallet,decred/dcrwallet