Settings/Oobe: Simplify cr-network-select and use flex

chrome/app/settings_strings.grdp

 <?xml version="1.0" encoding="utf-8"?>
 <!-- Settings-specific strings (included from generated_resources.grd). -->
 <grit-part>
   <!-- About Page -->
   <message name="IDS_SETTINGS_ABOUT_PAGE_BROWSER_VERSION" desc="The text label describing the version of the browser, example: Version 57.0.2937.0 (Developer Build) unknown (64-bit)">
     Version <ph name="PRODUCT_VERSION">$1<ex>15.0.865.0</ex></ph> (<ph name="PRODUCT_CHANNEL">$2<ex>Developer Build</ex></ph>) <ph name="PRODUCT_MODIFIER">$3</ph> <ph name="PRODUCT_VERSION_BITS">$4</ph>
   </message>
   <if expr="chromeos">
     <message name="IDS_SETTINGS_ABOUT_PAGE_DETAILED_BUILD_INFO" desc="Label describing the section that shows detailed information about the current Chrome build.">
       Detailed build information
@@ skipping 1238 matching lines @@
       Preferred networks will be preferred over other known networks if more than one is available.
     </message>
     <message name="IDS_SETTINGS_INTERNET_KNOWN_NETWORKS_ALL" desc="Title for list of all other (non preferred) networks.">
       All networks
     </message>
 
     <!-- Strings used in <cr-network-list>, used in Settings and OOBE -->
     <message name="IDS_NETWORK_LIST_DISABLED" desc="Settings > Internet, text in network summary when the network type is connected">
       Disabled
     </message>
-    <message name="IDS_NETWORK_LIST_EXPAND_ACCESSIBILITY_LABEL" desc="Label for the button that toggles showing the list of available network connections. Only visible by screen reader software.">
-      Show available network connections
-    </message>
     <message name="IDS_NETWORK_LIST_NOT_CONNECTED" desc="Settings > Internet, text in network summary when there is no network for the type.">
       No network
     </message>
     <message name="IDS_NETWORK_LIST_CONNECTED" desc="Settings > Internet, text to show in a network list item that is connected.">
       connected
     </message>
     <message name="IDS_NETWORK_LIST_CONNECTING" desc="Settings > Internet, text in network summary when the primary network is connecting.">
       Connecting to <ph name="NAME">$1<ex>GoogleGuest</ex></ph>
     </message>
     <message name="IDS_NETWORK_LIST_THIRD_PARTY_VPN_NAME_TEMPLATE" desc="Template for constructing the name of a VPN network that is handled by a third-party VPN provider from the provider name and the network name.">
@@ skipping 1483 matching lines @@
       System
     </message>
     <message name="IDS_SETTINGS_SYSTEM_HARDWARE_ACCELERATION_LABEL" desc="Label for the checkbox that forces Chrome to render via hardware acceleration (GPU) when available.">
       Use hardware acceleration when available
     </message>
     <message name="IDS_SETTINGS_SYSTEM_PROXY_SETTINGS_BUTTON" desc="Text for the button that changes a user's network proxy settings.">
       Change proxy settings
     </message>
   </if>
 </grit-part>