LibWeb: Use doubles for CSS dimension types

Avoid unintentionally converting between float and double multiple times
by just using double everywhere. Also, remove the unused `int` versions
of their constructors.

Userland/Libraries/LibWeb/CSS/Length.h

@@ -83,7 +83,6 @@ public:
 
     static Optional<Type> unit_from_name(StringView);
 
-    Length(int value, Type type);
     Length(double value, Type type);
     ~Length();