Remove declaration of undefined function __getDynamicPointerType. NFC (#18271)

I believe this function was removed from the codebase in
78568fe.

Author: sbc100

site/source/docs/api_reference/bind.h.rst

@@ -134,13 +134,7 @@ select_overload and select_const
 
 
 Functions
-=============
-
-.. cpp:function:: void* __getDynamicPointerType(void* p)
-
-
-   :param void* p
-
+=========
 
 .. cpp:function:: void function()
 

system/include/emscripten/bind.h

@@ -502,8 +502,6 @@ EMSCRIPTEN_ALWAYS_INLINE const char* getSignature(Return (*)(Args...)) {
 // FUNCTIONS
 ////////////////////////////////////////////////////////////////////////////////
 
-extern "C" void* __getDynamicPointerType(void* p);
-
 template<typename ReturnType, typename... Args, typename... Policies>
 void function(const char* name, ReturnType (*fn)(Args...), Policies...) {
     using namespace internal;