web_renderjs_ui: update comments about the reason for not using cache.addAll

The main reason for not using cache.addAll was to fill the cache as a low
priority task, not to generate too much traffic, the safari compatibility
was secondary. Now that safari seems to support cache.addAll, remove the
comment about safari.
2 jobs for <span class="ref-name">fix/cache.addAll-comment</span> in 0 seconds
Status Job ID Name Coverage
  External
passed ERP5.CodingStyleTest-TestRunner2

00:54:19

failed ERP5.UnitTest-TestRunner2

01:44:13