Remove background image

Unsure about copyright issues using it, the image is from the Strawbs boxset, removing
it for now.

data/data.qrc

@@ -9,7 +9,6 @@
         <file>misc/playing_tooltip.txt</file>
         <file>misc/oauthsuccess.html</file>
         <file>pictures/strawberry.png</file>
-        <file>pictures/strawbs-transparent.png</file>
         <file>pictures/noalbumart.png</file>
         <file>pictures/nomusic.png</file>
         <file>pictures/musicbrainz.png</file>

data/style/strawberry.css

@@ -4,7 +4,6 @@
 }
 
 #playlist[default_background_enabled = "true"] {
-  background-image: url(:pictures/strawbs-transparent.png);
   background-attachment: fixed;
   background-position: bottom right;
   background-repeat: none;