Revert of Add TabContainer to Showcase

ios/showcase/tab/BUILD.gn

-# Copyright 2017 The Chromium Authors. All rights reserved.
-# Use of this source code is governed by a BSD-style license that can be
-# found in the LICENSE file.
-
-source_set("tab") {
-  sources = [
-    "sc_bottom_toolbar_tab_coordinator.h",
-    "sc_bottom_toolbar_tab_coordinator.mm",
-    "sc_top_toolbar_tab_coordinator.h",
-    "sc_top_toolbar_tab_coordinator.mm",
-  ]
-  deps = [
-    "//base",
-    "//ios/clean/chrome/browser/ui/commands",
-    "//ios/clean/chrome/browser/ui/tab:tab_ui",
-    "//ios/showcase/common",
-  ]
-  libs = [ "UIKit.framework" ]
-  configs += [ "//build/config/compiler:enable_arc" ]
-}
-
-source_set("eg_tests") {
-  testonly = true
-  sources = [
-    "sc_tab_egtest.mm",
-  ]
-  deps = [
-    "//ios/showcase/test",
-    "//ios/third_party/earl_grey",
-  ]
-  libs = [ "XCTest.framework" ]
-  configs += [ "//build/config/compiler:enable_arc" ]
-}