refactor(dia.Link)!: remove smooth and manhattan attributes

[kumilingus]

Description

• removing the deprecated smooth attribute (syntactic sugar for the smooth connector).
• removing the obsolete manhattan attribute (syntactic sugar for orthogonal router).

Migration guide

Before:

link.set('smooth', true);
link.set('manhattan', true);

Now:

link.connector('smooth'); // or link.set('connector', { name: 'smooth' });
link.router('orthogonal'); // or link.set('router', { name: 'orthogonal' });