[REF] qweb: mostly revert fix with t-call and vars with body

The previous fix (overriding tostring of VDomArray) is actually more
general, and solves the same issue. So, let us simplify the code and
keep the more general solution.

This reverts commit 3bf91afc3f.

tests/component/component.test.ts

@@ -1766,7 +1766,6 @@ describe("props evaluation ", () => {
     await widget.mount(fixture);
     expect(fixture.innerHTML).toBe("<div><span>&lt;p&gt;4343&lt;/p&gt;<p>43</p></span></div>");
   });
-
 });
 
 describe("other directives with t-component", () => {