[fuchsia] Remove visibility hack from cast_runner_browsertests.

A visibility rule applying to cast_runner_browsertests__exec was added
in https://chromium-review.googlesource.com/c/chromium/src/+/1529685

Making assumptions about the naming of targets defined inside templates
is fragile, and this dependency isn't required, so remove it and the
associated visibility rule.

Bug: 933617
Change-Id: If05af64d54944b7cafb403aae3036981ca1e0698
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2050306
Commit-Queue: Wez <wez@chromium.org>
Commit-Queue: Fabrice de Gans-Riberi <fdegans@chromium.org>
Reviewed-by: Fabrice de Gans-Riberi <fdegans@chromium.org>
Auto-Submit: Wez <wez@chromium.org>
Cr-Commit-Position: refs/heads/master@{#741572}

fuchsia/engine/BUILD.gn

@@ -180,10 +180,7 @@ component("web_engine_core") {
     "web_engine_main_delegate.cc",
     "web_engine_main_delegate.h",
   ]
-  visibility = [
-    ":*",
-    "//fuchsia/runners:cast_runner_browsertests__exec",
-  ]
+  visibility = [ ":*" ]
 }
 
 source_set("switches") {

fuchsia/runners/BUILD.gn

@@ -180,7 +180,6 @@ test("cast_runner_browsertests") {
     "//fuchsia/base",
     "//fuchsia/base:test_support",
     "//fuchsia/engine:browsertest_core",
-    "//fuchsia/engine:web_engine_core",
     "//testing/gmock",
     "//testing/gtest",
     "//ui/ozone",