Remove deprecated emptyM3 function

[linuswagner]

Roughly 7 years ago, the function public M3 emptyM3(loc id) has been marked as deprecated. In addition, the comment //TODO: Deprecated method, replace any calls to this function with default constructor has added.

At the moment, Rascal itself does not have any dependencies on that function. The function should be removed because of that. Other libraries that depend on Rascal should be checked if they still use that function and if so, changed accordingly.

If this is not happening anytime soon, the deprecation should be documented as it is for some other functions:

@pitfalls{
:::warning
This function is *deprecated*, use the default constructor for M3 instead.
:::
}