Fixed the background color of "disabled code" in the grayscale scheme

This background color is also used for right margin background and
folded code popup. Not setting any resulted in weird affects in those
places.

share/qtcreator/styles/grayscale.xml

@@ -5,7 +5,6 @@
   <style name="CurrentLine" foreground="#000000" background="#f2f2f2"/>
   <style name="DiffFile"/>
   <style name="DiffLocation"/>
-  <style name="DisabledCode" foreground="#a0a0a4"/>
   <style name="Doxygen.Comment" foreground="#808080"/>
   <style name="Doxygen.Tag" foreground="#808080" italic="true"/>
   <style name="Keyword" bold="true"/>
@@ -24,6 +23,7 @@
   Relying on default colors for:
 
   CurrentLineNumber
+  DisabledCode
   LineNumber
   SearchResult
   SearchScope