LibJS: Use new format functions everywhere

This changes the remaining uses of the following functions across LibJS:

- String::format() => String::formatted()
- dbg() => dbgln()
- printf() => out(), outln()
- fprintf() => warnln()

I also removed the relevant 'LogStream& operator<<' overloads as they're
not needed anymore.

Libraries/LibJS/Runtime/Cell.cpp

@@ -24,7 +24,6 @@
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
-#include <AK/LogStream.h>
 #include <LibJS/Heap/Heap.h>
 #include <LibJS/Heap/HeapBlock.h>
 #include <LibJS/Runtime/Cell.h>
@@ -56,11 +55,4 @@ VM& Cell::vm() const
     return heap().vm();
 }
 
-const LogStream& operator<<(const LogStream& stream, const Cell* cell)
-{
-    if (!cell)
-        return stream << "Cell{nullptr}";
-    return stream << cell->class_name() << '{' << static_cast<const void*>(cell) << '}';
-}
-
 }