Disable unnecessary selection for all OOBE screens

Bug: 924497
Change-Id: I5c3d74e0f7e92662dc7138f0f7739ded544fe38a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2207464Reviewed-by: Denis Kuznetsov [CET] <antrim@chromium.org>
Reviewed-by: Roman Sorokin [CET] <rsorokin@chromium.org>
Commit-Queue: Jana Grill <janagrill@chromium.org>
Cr-Commit-Position: refs/heads/master@{#771726}

chrome/browser/resources/chromeos/login/oobe_eula.css

@@ -62,6 +62,7 @@ cr-checkbox {
   color: rgb(66, 133, 244);
   font-size: 24px;
   margin-top: 82px;
+  user-select: text;
 }
 
 .installation-settings-spinner {

chrome/browser/resources/chromeos/login/oobe_screen.css

@@ -12,6 +12,7 @@
 .step {
   box-sizing: border-box;
   position: absolute;
+  user-select: none;
 }
 
 .step.animated:not(.faded) {