revert r111028 (attempt to fix bug 34254)

That patch was obviously wrong, it disabled compression for any
requests *blushes*  :-]

RELEASE-NOTES-1.20

@@ -21,8 +21,6 @@ production.
 * (bug 30245) Use the correct way to construct a log page title.
 * (bug 34237) Regenerate an empty user_token and save to the database
   when we try to set the user's cookies for login.
-* (bug 34254) Using a gzipped file cache ($wgUseGzip and $wgUseFileCache)
-  compressed the output twice resulting in garbage output (since 1.18)
 * (bug 32210) New edit emails for watched pages always provide a link to the
   edit which triggered the mail.
 * (bug 12021) Added user talk link on Special:Listusers

includes/Setup.php

@@ -388,12 +388,6 @@ if ( $wgCanonicalServer === false ) {
 	$wgCanonicalServer = wfExpandUrl( $wgServer, PROTO_HTTP );
 }
 
-if ( $wgUseFileCache && $wgUseGzip ) {
-	// Bypass any previous output handler to avoid double
-	// compression (bug 34254)
-	wfResetOutputBuffers();
-}
-
 wfProfileIn( $fname . '-misc1' );
 
 # Raise the memory limit if it's too low