Revert of Made surrounding text work for last word in a document (patchset #5 id:80001 of https://codereview.chromium.org/2928073002/ )

Reason for revert:
This has caused the surrounding-text.html layout test to start failing on some bots. See for example:

https://uberchromegw.corp.google.com/i/chromium.webkit/builders/WebKit%20Linux%20Trusty/builds/28157

Original issue's description:
> Made surrounding text work for last word in a document
>
> The surrounding text algorithm did not proceed if the range
> between the end of selection and the end of document had zero
> length. Current CL removes this restriction.
>
> BUG=
>
> Review-Url: https://codereview.chromium.org/2928073002
> Cr-Commit-Position: refs/heads/master@{#482719}
> Committed: https://chromium.googlesource.com/chromium/src/+/445e7e4dc4bb49245a40b102bf3b3906dfcd6661

TBR=yosin@chromium.org,amaralp@chromium.org,timav@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=

Review-Url: https://codereview.chromium.org/2955973007
Cr-Commit-Position: refs/heads/master@{#482839}
4 files changed