[CS] Avoid CA2200 warning when rethrowing

[kLabz]

Code like that:

try {
	throw something;
} catch (eof:haxe.io.Eof) {}

Generates:

try {
	// ...
}
catch (global::System.Exception _g){
	if (( ((object) (global::haxe.Exception.caught(_g).unwrap()) ) is global::haxe.io.Eof )) {
	}
	else {
		throw _g;
	}
	
}

Which results in a runtime warning from C#:

warning CA2200: Re-throwing caught exception changes stack information

According to https://docs.microsoft.com/en-us/dotnet/fundamentals/code-analysis/quality-rules/ca2200, throw _g here should be just throw.

Note: this warning is currently generated with haxe std (haxe.io.Input) too