Revert "Make a duplicate class OSMHeaderBlock that contains the same header data. Deprecate the old HeaderBlock."

Keep the old name.

This reverts commit 0618651553.

src/osmformat.proto

@@ -35,19 +35,8 @@ coding when representing nodes and relations.
 //////////////////////////////////////////////////////////////////////////
 
 /* Contains the file header. */
-// DEPRECIATED CLASS NAME.
+
 message HeaderBlock {
-  optional HeaderBBox bbox = 1 [deprecate=true];
-  /* Additional tags to aid in parsing this dataset */
-  repeated string required_features = 4 [deprecate=true];
-  repeated string optional_features = 5 [deprecate=true];
-
-  optional string writingprogram = 16 [deprecate=true]; 
-  optional string source = 17 [deprecate=true]; // From the bbox field.
-}
-
-// Duplicate the above definition under a new class name.
-message OSMHeaderBlock {
   optional HeaderBBox bbox = 1;
   /* Additional tags to aid in parsing this dataset */
   repeated string required_features = 4;