Remove duplicate imports in settings UI

Remove duplicate import("//tools/polymer/polymer.gni") from some
BUILD.gn files in settings UI. This is a clean up work done while
creating a new settings section called Kerberos. See associated bug for
additional information.

Bug: 983041
Change-Id: Idbf0f78253d4f0410ea9600dff98ae9ac0bc9760
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2536648
Commit-Queue: Felipe Andrade <fsandrade@chromium.org>
Reviewed-by: Kyle Horimoto <khorimoto@chromium.org>
Cr-Commit-Position: refs/heads/master@{#828184}

chrome/browser/resources/settings/chromeos/os_people_page/BUILD.gn

@@ -518,8 +518,6 @@ js_library("users_page.m") {
   extra_deps = [ ":users_page_module" ]
 }
 
-import("//tools/polymer/polymer.gni")
-
 group("polymer3_elements") {
   public_deps = [
     ":account_manager_module",

chrome/browser/resources/settings/chromeos/os_printing_page/BUILD.gn

@@ -360,8 +360,6 @@ js_library("os_printing_page.m") {
   extra_deps = [ ":os_printing_page_module" ]
 }
 
-import("//tools/polymer/polymer.gni")
-
 group("polymer3_elements") {
   public_deps = [
     ":cups_add_print_server_dialog_module",

chrome/browser/resources/settings/settings_page/BUILD.gn

@@ -105,8 +105,6 @@ js_library("settings_subpage.m") {
   extra_deps = [ ":settings_subpage_module" ]
 }
 
-import("//tools/polymer/polymer.gni")
-
 group("polymer3_elements") {
   public_deps = [
     ":settings_animated_pages_module",