Temporarily disabled testing 56000 baud
Temporarily disabled testing 56000 baud

Due to a regression in mbed-os, the daplink-validation program
no longer supports 56000 baud on the nrf5x targets. Temporarily
remove this baudrate so DAPLink PRs can be tested and merged.

sg-/DAPLink,google/DAPLink-port,sg-/DAPLink,google/DAPLink-port,sg-/DAPLink,google/DAPLink-port,google/DAPLink-port