[CI][Docs][MATLAB] Remove support for `MATLAB_ARROW_INTERFACE` flag from CMake build system and build new MATLAB Interface code by default

[kevingurney]

Describe the enhancement requested

Now that the old Feather V1 code and associated build infrastructure has been removed (#37204), it would make sense to start building the new, experimental MATLAB Interface code by default (without needing to explicitly specify -D MATLAB_ARROW_INTERFACE=ON).

If we start building the MATLAB Interface code by default, it would also make sense to remove the MATLAB_ARROW_INTERFACE flag entirely, since setting it to OFF would essentially imply that no code should be built.

Component(s)

MATLAB

[kevingurney]

Added label Component: Continuous Integration since resolving this involves updating the matlab_build.sh CI script to no longer specify -D MATLAB_ARROW_INTERFACE=ON.

[kevingurney]

Added label Component: Documentation since resolving this involves updating the MATLAB README.md to no longer mention the -D MATLAB_ARROW_INTERFACE=ON flag.