TestSink GUI cosmetic change

plugins/samplesink/testsink/testsinkgui.ui

@@ -294,12 +294,6 @@
    </item>
    <item>
     <layout class="QVBoxLayout" name="spectrumLayout">
-     <property name="topMargin">
-      <number>6</number>
-     </property>
-     <property name="bottomMargin">
-      <number>6</number>
-     </property>
      <item>
       <widget class="GLSpectrum" name="glSpectrum" native="true">
        <property name="minimumSize">