Don't add `external` modifier to fallback functions

[fvictorio]

This:

contract Foo {
  fallback() {}
}

when formatted, gets an added external modifier. This is useful in a lot of situations, but I don't think we should do it. In the same vein as issues like #662, we should avoid making this kind of non-strictly-formatting change.

[Janther]

the printer doesn't make that decision. We print exactly the visibility that the parser gives us.

prettier-plugin-solidity/src/nodes/FunctionDefinition.js

Line 110 in f927935

visibility(node),

prettier-plugin-solidity/src/nodes/FunctionDefinition.js

Lines 57 to 60 in f927935

	const visibility = (node) =>
	node.visibility && node.visibility !== 'default'
	? [line, node.visibility]
	: '';

[fvictorio]

I will open an issue in the parser about this.

[fvictorio]

solidity-parser/parser#76