Revert "Turn on Polymer v2 on OOBE by default"

This reverts commit 57d362b5.

Reason for revert: test failures on https://ci.chromium.org/p/chromium/builders/ci/Linux%20ChromiumOS%20MSan%20Tests?limit=100, several of which seem related to OOBE

Original change's description:
> Turn on Polymer v2 on OOBE by default
> 
> Bug: 955194
> Change-Id: I6581822689118b554107689e3cbca29b16d240df
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2080427
> Reviewed-by: Roman Sorokin [CET] <rsorokin@chromium.org>
> Reviewed-by: Scott Violet <sky@chromium.org>
> Commit-Queue: Denis Kuznetsov [CET] <antrim@chromium.org>
> Auto-Submit: Denis Kuznetsov [CET] <antrim@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#745923}

TBR=sky@chromium.org,antrim@chromium.org,rsorokin@chromium.org

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: 955194
Change-Id: I46cd070a5162d18ce8ff41cf892ccebfe11340b8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2090801Reviewed-by: Collin Baker <collinbaker@chromium.org>
Commit-Queue: Collin Baker <collinbaker@chromium.org>
Cr-Commit-Position: refs/heads/master@{#747873}

content/public/common/content_features.cc

@@ -856,7 +856,7 @@ const base::Feature kWebNfc{"WebNFC", base::FEATURE_ENABLED_BY_DEFAULT};
 // TODO(crbug.com/955194): Remove this once chrome://oobe migrates off of
 // Polymer 1.
 const base::Feature kWebUIPolymer2Exceptions{"WebUIPolymer2Exceptions",
-                                             base::FEATURE_DISABLED_BY_DEFAULT};
+                                             base::FEATURE_ENABLED_BY_DEFAULT};
 #endif  // defined(OS_CHROMEOS)
 
 #if defined(OS_MACOSX)