Removal of `mtb4fap` board

[marcoaccame]

This PR is associated w/ others (see below) which remove the board mtb4fap from robotology because its functionalities are offered by the mtb4c.

Associated PRs:

• https://github.com/robotology/icub-firmware-shared/pull/80
• https://github.com/robotology/icub-firmware/pull/359
• https://github.com/robotology/icub-main/pull/860
• https://github.com/robotology/robots-configuration/pull/459
• https://github.com/robotology/icub-firmware-build/pull/76