Update signin string per Android UXW style

Update "No Thanks" to "No thanks" per Android UXW style.

Bug: 986687
Change-Id: I43bf4a607147423d04873e2aa55a3b9135a3507a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1715277Reviewed-by: Colin Blundell <blundell@chromium.org>
Commit-Queue: Tanmoy Mollik <triploblastic@google.com>
Cr-Commit-Position: refs/heads/master@{#680541}

chrome/android/java/strings/android_chrome_strings.grd

@@ -195,7 +195,7 @@ CHAR-LIMIT guidelines:
         Close
       </message>
       <message name="IDS_NO_THANKS" desc="Generic label to say no thanks for a feature. [CHAR-LIMIT=32]">
-        No Thanks
+        No thanks
       </message>
       <message name="IDS_NEXT" desc="Generic label for a button to advance to the next item. [CHAR-LIMIT=20]">
         Next

chrome/android/java/strings/android_chrome_strings_grd/IDS_NO_THANKS.png.sha1

+8d608c5930d162c144c209daea9ac6238edb68e2
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