AP_RangeFinder: Remove preprocessor in enum definition

[muramura]

ENUM definitions do not consume memory.
This ENUM definition is used only for the SWITCH statement.
Adding DEFAULT to the SWITCH statement suppresses errors for undefined definitions.
There are many preprocessors with ENUM definitions that are undefined.
I remove preprocessors in the ENUM definition.

[peterbarker]

You're correct that the enumerations don't take up space.

However, as a pattern removing the values from the enumeration if the driver is not compiled in means that no code which is dependent on that enumeration entry can remain in the code when the compiler is not compiled in - it's a code-cleanliness enhancer.

We're moving to use this pattern - not away from it.