hexview: drop 'override' on comment() for QHexView <v5.1.0 compat

QHexDelegate::comment() virtual was added to QHexView after the v5.1.0
tag. Building against v5.1.0 fails with:

  error: 'QString FlagsDelegate::comment(...)' marked 'override',
         but does not override

Remove the override specifier so the code compiles against released
QHexView versions. The comment() feature will be a no-op until QHexView
ships a tagged release with the virtual.

Author: blshkv

src/hexview/flagsdelegate.h

@@ -12,9 +12,9 @@ class FlagsDelegate: public QHexDelegate {
 
 public:
     QString comment(quint64 offset, quint8 b,
-                    const QHexView* hexview) const override;
+                    const QHexView* hexview) const;
     bool renderByte(quint64 offset, quint8 b, QHexCharFormat& outcf,
-                    const QHexView* hexview) const override;
+                    const QHexView* hexview) const;
 
 private:
     const RDFlagsBuffer* m_flags{nullptr};