change _change_pin_internal to change_pin_internal to match style
change _change_pin_internal to change_pin_internal to match style

all other internal functions have plain names

akgood/yubico-piv-tool,Yubico/yubico-piv-tool,akgood/yubico-piv-tool,akgood/yubico-piv-tool,Yubico/yubico-piv-tool,Yubico/yubico-piv-tool,akgood/yubico-piv-tool