[FIX] qweb: do not capture current qweb instance in closure

it is not needed, and has a bad effect on globally registered templates.

tests/qweb/__snapshots__/qweb.test.ts.snap

@@ -1118,6 +1118,21 @@ exports[`t-call (template calling t-call with t-if 1`] = `
 }"
 `;
 
+exports[`t-call (template calling t-call, global templates 1`] = `
+"function anonymous(context,extra
+) {
+    var h = this.h;
+    let c1 = [], p1 = {key:1};
+    var vn1 = h('div', p1, c1);
+    result = vn1;
+    let c2 = [], p2 = {key:2};
+    var vn2 = h('span', p2, c2);
+    c1.push(vn2);
+    c2.push({text: \`desk\`});
+    return vn1;
+}"
+`;
+
 exports[`t-call (template calling with unused body 1`] = `
 "function anonymous(context,extra
 ) {