LibWeb: Stop including StyleValue.h in a few places

I don't know how much this will actually help compile times, but it's
something!

Userland/Libraries/LibWeb/CSS/LengthBox.h

@@ -6,8 +6,7 @@
 
 #pragma once
 
-#include <LibWeb/CSS/Length.h>
-#include <LibWeb/CSS/StyleValue.h>
+#include <LibWeb/CSS/Percentage.h>
 
 namespace Web::CSS {
 

Userland/Libraries/LibWeb/HTML/HTMLBlinkElement.cpp

@@ -5,7 +5,6 @@
  */
 
 #include <LibCore/Timer.h>
-#include <LibWeb/CSS/StyleValue.h>
 #include <LibWeb/HTML/HTMLBlinkElement.h>
 
 namespace Web::HTML {

Userland/Libraries/LibWeb/Layout/ImageBox.cpp

@@ -5,7 +5,6 @@
  */
 
 #include <LibGfx/Font/FontDatabase.h>
-#include <LibWeb/CSS/StyleValue.h>
 #include <LibWeb/HTML/BrowsingContext.h>
 #include <LibWeb/Layout/ImageBox.h>
 #include <LibWeb/Painting/ImagePaintable.h>

Userland/Libraries/LibWeb/Painting/BackgroundPainting.h

@@ -7,7 +7,6 @@
 #pragma once
 
 #include <LibGfx/Forward.h>
-#include <LibWeb/CSS/StyleValue.h>
 #include <LibWeb/Forward.h>
 #include <LibWeb/Painting/BorderPainting.h>
 #include <LibWeb/Painting/PaintContext.h>