feat(upgrade): fix support for directive.link in upgraded components

(#17971)

Although, pre- and post-linking functions are correctly called during directive
linking, directives with `link.post` would throw an error. Interestingly, having
`link.pre` only or defining `link: fn` (which is an alias for `link.post: fn`)
would not throw.

This commit removes this check and allows directives with pre- and/or
post-linking functions to work.

packages/upgrade/src/common/upgrade_helper.ts

@@ -90,12 +90,6 @@ export class UpgradeHelper {
     if (directive.terminal) this.notSupported('terminal');
     if (directive.compile) this.notSupported('compile');
 
-    const link = directive.link;
-    // QUESTION: why not support link.post?
-    if (typeof link == 'object') {
-      if (link.post) this.notSupported('link.post');
-    }
-
     return directive;
   }