Remove ambiguous case for constructing pros::Task

[jm-spencer]

Summary:

There is an ambiguous case for construction of pros::Task when only 1 or 2 parameters are specified. This is fixed by removing the defaults on the 2nd and 3rd params.

Motivation:

As is, task construction when only the function and/or task parameter is specified is not allowed.

References (optional):

I accidentally introduced this in #158

Test Plan:

Make sure a Task object can be created while only specifying the function. Example:

void func(void* param){
    std::cout << "This task is running\n";
}

pros::Task task(func);

• test item

[HotelCalifornia]

I wonder how this interacts with #177

[jm-spencer]

Looks like #177 doesn't interact with the shortened constructor at all.

[nathan-moore]

There's no breaking change that I see, so looks good to me.