Remove QtCore QDoc warning limit again

It was set to two (2) due to QTBUG-126546, but wasn't reset after
qttools/7c2fc7687f653a6002c93720bc6d52827390a6d1 merged, which fixed
said bug report.

Reverts cec4705.

Not picking to 6.8, because the qdoc fix wasn't.

Task-number: QTBUG-126546
Change-Id: I336ee7d3c1e7d2b14a2768aae20128ebfae0efbf
Reviewed-by: Paul Wicking <paul.wicking@qt.io>

src/corelib/doc/qtcore.qdocconf

@@ -73,5 +73,4 @@ manifestmeta.highlighted.names = \
     "QtCore/Serialization Converter" \
     "QtCore/QXmlStream Bookmarks Example"
 
-# QTBUG-126546
-warninglimit = 2
+warninglimit = 0