Various plugins: Remove unused variables

Found by Axivion plugin.

Change-Id: I628b00e4525b004c702dd8753af31cb3fedf1739
Reviewed-by: Christian Kandeler <christian.kandeler@qt.io>

src/plugins/coreplugin/welcomepagehelper.cpp

@@ -851,7 +851,6 @@ void ListItemDelegate::paint(QPainter *painter, const QStyleOptionViewItem &opti
     const QFont tagsLabelFont = tagsLabelTF.font();
     const QFontMetrics tagsLabelFM(tagsLabelFont);
     const QFont descriptionFont = descriptionTF.font();
-    const QFontMetrics descriptionFM(descriptionFont);
 
     const QRect bgRGlobal = option.rect.adjusted(0, 0, -ExVPaddingGapXl, -ExVPaddingGapXl);
     const QRect bgR = bgRGlobal.translated(-option.rect.topLeft());

src/plugins/projectexplorer/toolchainsettingsaccessor.cpp

@@ -254,7 +254,6 @@ void ToolchainSettingsAccessor::saveToolchains(const Toolchains &toolchains, QWi
 Toolchains ToolchainSettingsAccessor::toolChains(const Store &data) const
 {
     Toolchains result;
-    const QList<ToolchainFactory *> factories = ToolchainFactory::allToolchainFactories();
 
     const int count = data.value(TOOLCHAIN_COUNT_KEY, 0).toInt();
     for (int i = 0; i < count; ++i) {

src/plugins/texteditor/semantichighlighter.cpp

@@ -161,7 +161,6 @@ void SemanticHighlighter::clearExtraAdditionalFormatsUntilEnd(
         }
     }
 
-    QList<int> clearBlockNumberVector;
     for (QTextBlock b = firstBlockToClear; b.isValid(); b = b.next())
         highlighter->clearExtraFormats(b);