Refactor embedded assets and drop unnecessary dependencies (#34692)

Benefits:

1. smaller binary size (reduces more than 1MB)
2. better control of the assets details
3. fewer unmaintained dependencies
4. faster startup if the assets are not needed
5. won't hang up editors when open "bindata.go" by accident

modules/migration/schemas_bindata.go

@@ -3,6 +3,28 @@
 
 //go:build bindata
 
+//go:generate go run ../../build/generate-bindata.go ../../modules/migration/schemas bindata.dat
+
 package migration
 
-//go:generate go run ../../build/generate-bindata.go ../../modules/migration/schemas migration bindata.go
+import (
+	"io"
+	"io/fs"
+	"path"
+	"sync"
+
+	_ "embed"
+
+	"code.gitea.io/gitea/modules/assetfs"
+)
+
+//go:embed bindata.dat
+var bindata []byte
+
+var BuiltinAssets = sync.OnceValue(func() fs.FS {
+	return assetfs.NewEmbeddedFS(bindata)
+})
+
+func openSchema(filename string) (io.ReadCloser, error) {
+	return BuiltinAssets().Open(path.Base(filename))
+}