Fix unused-parameter warning

[ardabbour]

When building a package that uses this header, the compiler throws this unused parameter warning (and rightly so). This solution is probably incompatiable with Windows, so if intercompatiability is an issue, perhaps [[maybe_unused]] should be used instead, but that requires C++17: More here

[Timple]

Otherwise

double& Long, double& /*gamma*/)

might be an option as well.

[SteveMacenski]

@Timple's suggestion is more in line with standard practice, if you wouldn't mind making that update? You'd do that in the cpp file, not the header file.

[ardabbour]

There is no navsat_conversions.cpp seperate from the header (or I'm missing something), but I've changed it to the standard practice; should do the trick

[Timple]

Nitpick: the comment already suggests that the code is unused. Leaving the word gamma also indicates what is unused.

[ayrton04]

Thanks!