Removed unused `_upb_DefPool_registerlayout()` function.

This function was introduced in https://github.com/protocolbuffers/upb/pull/426 but it appears it was never used.  I am not sure what the purpose was, but in any case it is not needed.

With this function removed, we no longer need to tag pointers for the DefPool "files" table.

PiperOrigin-RevId: 470567000

upb/def.c

@@ -239,7 +239,6 @@ typedef enum {
 
   /* Only inside file table. */
   UPB_DEFTYPE_FILE = 0,
-  UPB_DEFTYPE_LAYOUT = 1
 } upb_deftype_t;
 
 #define FIELD_TYPE_UNSPECIFIED 0
@@ -1208,8 +1207,7 @@ const upb_EnumValueDef* upb_DefPool_FindEnumByNameval(const upb_DefPool* s,
 const upb_FileDef* upb_DefPool_FindFileByName(const upb_DefPool* s,
                                               const char* name) {
   upb_value v;
-  return upb_strtable_lookup(&s->files, name, &v)
+  return upb_strtable_lookup(&s->files, name, &v) ? upb_value_getconstptr(v)
-             ? unpack_def(v, UPB_DEFTYPE_FILE)
                                                   : NULL;
 }
 
@@ -1218,7 +1216,7 @@ const upb_FileDef* upb_DefPool_FindFileByNameWithSize(const upb_DefPool* s,
                                                       size_t len) {
   upb_value v;
   return upb_strtable_lookup2(&s->files, name, len, &v)
-             ? unpack_def(v, UPB_DEFTYPE_FILE)
+             ? upb_value_getconstptr(v)
              : NULL;
 }
 
@@ -3131,21 +3129,10 @@ static const upb_FileDef* _upb_DefPool_AddFile(
   upb_value v;
 
   if (upb_strtable_lookup2(&s->files, name.data, name.size, &v)) {
-    if (unpack_def(v, UPB_DEFTYPE_FILE)) {
     upb_Status_SetErrorFormat(status, "duplicate file name (%.*s)",
                               UPB_STRINGVIEW_ARGS(name));
     return NULL;
   }
-    const upb_MiniTable_File* registered = unpack_def(v, UPB_DEFTYPE_LAYOUT);
-    UPB_ASSERT(registered);
-    if (layout && layout != registered) {
-      upb_Status_SetErrorFormat(
-          status, "tried to build with a different layout (filename=%.*s)",
-          UPB_STRINGVIEW_ARGS(name));
-      return NULL;
-    }
-    layout = registered;
-  }
 
   ctx.symtab = s;
   ctx.layout = layout;
@@ -3173,7 +3160,7 @@ static const upb_FileDef* _upb_DefPool_AddFile(
   } else {
     _upb_FileDef_Create(&ctx, file_proto);
     upb_strtable_insert(&s->files, name.data, name.size,
-                        pack_def(ctx.file, UPB_DEFTYPE_FILE), ctx.arena);
+                        upb_value_constptr(ctx.file), ctx.arena);
     UPB_ASSERT(upb_Status_IsOk(status));
     upb_Arena_Fuse(s->arena, ctx.arena);
   }
@@ -3266,14 +3253,6 @@ const upb_FieldDef* upb_DefPool_FindExtensionByNumber(const upb_DefPool* s,
   return ext ? _upb_DefPool_FindExtensionByMiniTable(s, ext) : NULL;
 }
 
-bool _upb_DefPool_registerlayout(upb_DefPool* s, const char* filename,
-                                 const upb_MiniTable_File* file) {
-  if (upb_DefPool_FindFileByName(s, filename)) return false;
-  upb_value v = pack_def(file, UPB_DEFTYPE_LAYOUT);
-  return upb_strtable_insert(&s->files, filename, strlen(filename), v,
-                             s->arena);
-}
-
 const upb_ExtensionRegistry* upb_DefPool_ExtensionRegistry(
     const upb_DefPool* s) {
   return s->extreg;