Remove/update Qt 5 to-do's that won't be done for Qt 5.

Task-number: QTBUG-23524
Change-Id: Iebf5b78dc2ff27310b5a484bae588862417f693c
Reviewed-by: Jędrzej Nowacki <jedrzej.nowacki@nokia.com>
Reviewed-by: João Abecasis <joao.abecasis@nokia.com>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/kernel/qvariant.cpp

@@ -1554,7 +1554,6 @@ void QVariant::detach()
     \internal
 */
 
-// ### Qt 5: change typeName()(and froends= to return a QString. Suggestion from Harald.
 /*!
     Returns the name of the type stored in the variant. The returned
     strings describe the C++ datatype used to store the data: for

src/corelib/tools/qbitarray.h

@@ -72,7 +72,6 @@ public:
     inline int size() const { return (d.size() << 3) - *d.constData(); }
     inline int count() const { return (d.size() << 3) - *d.constData(); }
     int count(bool on) const;
-    // ### Qt 5: Store the number of set bits separately
 
     inline bool isEmpty() const { return d.isEmpty(); }
     inline bool isNull() const { return d.isNull(); }

src/corelib/tools/qstring.cpp

@@ -5056,7 +5056,7 @@ QString QString::toUpper() const
     return *this;
 }
 
-// ### Qt 5: Consider whether this function shouldn't be removed See task 202871.
+// ### Qt 6: Consider whether this function shouldn't be removed See task 202871.
 /*!
     Safely builds a formatted string from the format string \a cformat
     and an arbitrary list of arguments.