Do not use real message names in 'All_system_messages' preprocessor test

Do not use real message names in 'All_system_messages' preprocessor test

This file seems to be a stress-test for the MediaWiki preprocessor.
It doesn't really matter whether the messages references here exist.
As messages are occasionally renamed or deleted, and since this file
was generated in 2011, people keep getting confused when they grep
for a message name and run into this list (and sometimes needlessly
spend their time updating this file, as seen in its Git history).

This commit replaces all of the message names with their SHA1 hash
truncated to 8 hex characters.

Regexps used for matching:
(?<=\?title=MediaWiki\:)([^&{}<>|\[\]]+)
(?<=int:)([^&{}<>|\[\]]+)
(?<=\[\[MediaWiki_talk:)([^&{}<>|\[\]]+)
(?<=action=edit )([^&{}<>|\[\]]+)

Change-Id: I52a71c0cc0e6fa21a61420d52df755066c6e9a08