Remove unused CSS style from settings people / sync pages

"setting-box.middle" doesn't match anything.

Before:
http://screen/V28K1n5VXqZ
http://screen/MfXDMJpGHVt

After (unchanged):
http://screen/R6mUCiqbXpP
http://screen/U3Fc6LTTBNP

Bug: none
Change-Id: If741302d192b248c988d30aa892231cc252c189f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2079015
Commit-Queue: James Cook <jamescook@chromium.org>
Commit-Queue: Kyle Horimoto <khorimoto@chromium.org>
Auto-Submit: James Cook <jamescook@chromium.org>
Reviewed-by: Kyle Horimoto <khorimoto@chromium.org>
Cr-Commit-Position: refs/heads/master@{#745682}

chrome/browser/resources/settings/chromeos/os_people_page/os_people_page.html

@@ -37,11 +37,6 @@
 <dom-module id="os-settings-people-page">
   <template>
     <style include="settings-shared iron-flex">
-      setting-box.middle {
-        /* Per spec, middle text is indented 20px in this section. */
-        margin-inline-start: 20px;
-      }
-
       .sync-row {
         align-items: center;
         flex: auto;

chrome/browser/resources/settings/people_page/people_page.html

@@ -40,11 +40,6 @@
 <dom-module id="settings-people-page">
   <template>
     <style include="settings-shared iron-flex">
-      setting-box.middle {
-        /* Per spec, middle text is indented 20px in this section. */
-        margin-inline-start: 20px;
-      }
-
       .sync-row {
         align-items: center;
         flex: auto;

chrome/browser/resources/settings/people_page/sync_account_control.html

@@ -25,11 +25,6 @@
         --sync-icon-size: 16px;
       }
 
-      setting-box.middle {
-        /* Per spec, middle text is indented 20px in this section. */
-        margin-inline-start: 20px;
-      }
-
       .account-icon {
         border-radius: 20px;
         flex-shrink: 0;