Remove icon properties in .ui file with Designer's "." normaloff file data

Qt Designer (accidentally) injected "." file names as fallback when
setting theme icon names, which then results in generated code like:
    QIcon icon;
    QString iconThemeName = QString::fromUtf8("format-text-superscript");
    if (QIcon::hasThemeIcon(iconThemeName)) {
        icon = QIcon::fromTheme(iconThemeName);
    } else {
        icon.addFile(QString::fromUtf8("."), QSize(), QIcon::Normal, QIcon::Off);
    }
Such a "." file name is not documented to serve any purpose, just results
in failing icon lookup.

For the given UI elements the icons will be replaced in manual code later,
with more special code, so the properties can just be dropped.

See QTBUG-115333.

NO_CHANGELOG