Updates WORKSPACE to download locally versioned browsers.

Refs #74.

We _must_ drop the `@io_bazel_rules_webtesting` `browser_repositories` call because it will download to the same Bazel repository names and conflict with the locally versioned browsers.

WORKSPACE.bazel

@@ -56,9 +56,6 @@ load(
 )
 web_test_repositories()
 
-# Load web testing browsers and drivers (ie. Chrome and Chromedriver).
-load(
-    "@io_bazel_rules_webtesting//web/versioned:browsers-0.3.3.bzl",
-    "browser_repositories",
-)
-browser_repositories(chromium = True)
+# Load browser binaries.
+load("//bazel/browsers:browser_repositories.bzl", "browser_repositories")
+browser_repositories()