probe: drop support for PROTO_OPENOCD_CUSTOM CMSIS-DAP is a complete superset of the Picoprobe protocol, so now we default to DAPv2 there's no need to keep the downstream code. Also make setting up the reset pin conditional and in the correct place.
Picoprobe allows a Pico / RP2040 to be used as USB -> SWD and UART bridge. This means it can be used as a debugger and serial console for another Pico.
Picoprobe documentation can be found in the Pico Getting Started Guide. See “Appendix A: Using Picoprobe”.