Prepare WebCoreNSURLExtras for ARC

Prepare WebCoreNSURLExtras for ARC
https://bugs.webkit.org/show_bug.cgi?id=190219

Reviewed by Tim Horton.

ARC doesn't like the explicit sending of -release.
Use RetainPtr instead.

* platform/mac/WebCoreNSURLExtras.mm:
(WebCore::collectRangesThatNeedMapping):
(WebCore::collectRangesThatNeedEncoding):
(WebCore::collectRangesThatNeedDecoding):
(WebCore::applyHostNameFunctionToMailToURLString):
(WebCore::applyHostNameFunctionToURLString):
(WebCore::mapHostNames):
(WebCore::stringByTrimmingWhitespace):
(WebCore::URLWithUserTypedString):
(WebCore::userVisibleString):
(WebCore::rangeOfURLScheme):
(WebCore::looksLikeAbsoluteURL):
(WebCore::retain): Deleted.

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@236767 268f45cc-cd09-0410-ab3c-d52691b4dbfc