Remove the file_attribute macro

[matthewmcgarvey]

With the changes in b447938 the only thing file_attribute does is specify the type for you. Because I would prefer being able to define any type for an attribute this feels like a special case we shouldn't handle.

avram/src/avram/define_attribute.cr

Lines 91 to 97 in b447938

	macro file_attribute(key)
	{% unless key.is_a?(SymbolLiteral) %}
	{% raise "file_attribute must be declared with a Symbol" %}
	{% end %}
	attribute {{ key.id }} : Avram::Uploadable
	end

[jwoertink]

I think this is a nice addition still. It would be tough to remember the type if you wanted a file, but remembering file_attribute is pretty easy to remember. This would be different if we could say attribute doc : File or something, but in this case is special because it's not a built-in crystal type.

[matthewmcgarvey]

@jwoertink another nice thing about removing this is that it would be one step on the way to removing Avram::Uploadable which is just a thin integration layer for Lucky::UploadedFile