reflect/protoregistry: remove Files.Find{Enum,Message,Extension,Service}ByName

This is a breaking change.

The replacement is the Files.FindDescriptorByName method,
which is more flexible as it handles all descriptor types.

Change-Id: I2ccd544a7630396a2428b1d41f836c5246070912
Reviewed-on: https://go-review.googlesource.com/c/protobuf/+/183700
Reviewed-by: Damien Neil <dneil@google.com>
diff --git a/internal/filedesc/build.go b/internal/filedesc/build.go
index 28bd370..5f46e34 100644
--- a/internal/filedesc/build.go
+++ b/internal/filedesc/build.go
@@ -40,8 +40,7 @@
 	// If nil, it uses protoregistry.GlobalFiles.
 	FileRegistry interface {
 		FindFileByPath(string) (protoreflect.FileDescriptor, error)
-		FindEnumByName(pref.FullName) (pref.EnumDescriptor, error)
-		FindMessageByName(pref.FullName) (pref.MessageDescriptor, error)
+		FindDescriptorByName(pref.FullName) (pref.Descriptor, error)
 		Register(...pref.FileDescriptor) error
 	}
 }