LibWeb: Remove StyleProperties::set_property(PropertyID, StringView)

This API has no more clients (and the last client that I just removed
wasn't even using it right) so let's get rid of it.

Userland/Libraries/LibWeb/CSS/StyleProperties.cpp

@@ -39,11 +39,6 @@ void StyleProperties::set_property(CSS::PropertyID id, NonnullRefPtr<StyleValue>
     m_property_values.set(id, move(value));
 }
 
-void StyleProperties::set_property(CSS::PropertyID id, const StringView& value)
-{
-    m_property_values.set(id, StringStyleValue::create(value));
-}
-
 Optional<NonnullRefPtr<StyleValue>> StyleProperties::property(CSS::PropertyID property_id) const
 {
     auto it = m_property_values.find(property_id);

Userland/Libraries/LibWeb/CSS/StyleProperties.h

@@ -37,7 +37,6 @@ public:
     HashMap<CSS::PropertyID, NonnullRefPtr<StyleValue>> const& properties() const { return m_property_values; }
 
     void set_property(CSS::PropertyID, NonnullRefPtr<StyleValue> value);
-    void set_property(CSS::PropertyID, const StringView&);
     Optional<NonnullRefPtr<StyleValue>> property(CSS::PropertyID) const;
 
     Length length_or_fallback(CSS::PropertyID, const Length& fallback) const;