[UI] Enable themed *.png icons again for Linux

Reference: my first comment here: #761

src/qt/platformstyle.cpp

@@ -25,7 +25,7 @@ static const struct {
     {"macosx", false, false, true},
     {"windows", true, false, false},
     /* Other: linux, unix, ... */
-    {"other", true, true, false}
+    {"other", true, false, false}
 };
 static const unsigned platform_styles_count = sizeof(platform_styles)/sizeof(*platform_styles);