Removing assert in rtc_test template.

The assert causes a error when package default visibility is used.

Bug: None
Change-Id: I0d9006da8d838bd7113856bbf33fa2060c118f67
No-Try: True
Reviewed-on: https://webrtc-review.googlesource.com/24900
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Commit-Queue: Mirko Bonadei <mbonadei@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#20824}

webrtc.gni

@@ -266,9 +266,10 @@ template("rtc_test") {
                              "suppressed_configs",
                              "visibility",
                            ])
-    assert(
-        !defined(invoker.visibility),
-        "rtc_test always has visibility `*`; please don't specify it manually")
+
+    # Always override to public because when target_os is Android the `test`
+    # template can override it to [ "*" ] and we want to avoid conditional
+    # visibility.
     visibility = [ "*" ]
     configs += invoker.configs
     configs -= rtc_remove_configs