[FIX] mail: fix perf of models by removing useless onChange

onChange on each field is extremely costly, and it's not actually used
unless the field is computed or sorted.

Time of test "Load 100 recipients at once" is divied by more than 2.

Part-of: odoo/odoo#145442

addons/mail/static/src/core/common/record.js

@@ -238,7 +238,9 @@ export function makeStore(env) {
                             this[name] = defaultVal;
                         }
                         const rfield = toRaw(field);
-                        onChange(proxy, name, () => (rfield.changed = true));
+                        if (compute || sort) {
+                            onChange(proxy, name, () => (rfield.changed = true));
+                        }
                         if (compute) {
                             const proxy2 = reactive(proxy, () => rfield.requestCompute());
                             Object.assign(rfield, {