Remove unused wasm_runtime_is_module_registered (#1594)

It is unused and the same functionality is provided by
`wasm_runtime_find_module_registered`.

core/iwasm/common/wasm_runtime_common.c

@@ -702,12 +702,6 @@ wasm_runtime_find_module_registered(const char *module_name)
     return module ? module->module : NULL;
 }
 
-bool
-wasm_runtime_is_module_registered(const char *module_name)
-{
-    return NULL != wasm_runtime_find_module_registered(module_name);
-}
-
 /*
  * simply destroy all
  */

core/iwasm/common/wasm_runtime_common.h

@@ -718,9 +718,6 @@ wasm_runtime_register_module_internal(const char *module_name,
 void
 wasm_runtime_unregister_module(const WASMModuleCommon *module);
 
-bool
-wasm_runtime_is_module_registered(const char *module_name);
-
 bool
 wasm_runtime_add_loading_module(const char *module_name, char *error_buf,
                                 uint32 error_buf_size);