[core] Remove GRPC_INITIAL_METADATA_CORKED flag (#30443)

This functionality is entirely implemented in the C++ bindings layer, and so does not need a flag passed down to core (which core already ignores silently).

include/grpc/impl/codegen/grpc_types.h

@@ -524,14 +524,11 @@ typedef enum grpc_call_error {
 /** Signal that GRPC_INITIAL_METADATA_WAIT_FOR_READY was explicitly set
     by the calling application. */
 #define GRPC_INITIAL_METADATA_WAIT_FOR_READY_EXPLICITLY_SET (0x00000080u)
-/** Signal that the initial metadata should be corked */
-#define GRPC_INITIAL_METADATA_CORKED (0x00000100u)
 
 /** Mask of all valid flags */
-#define GRPC_INITIAL_METADATA_USED_MASK                                  \
-  (GRPC_INITIAL_METADATA_WAIT_FOR_READY_EXPLICITLY_SET |                 \
-   GRPC_INITIAL_METADATA_WAIT_FOR_READY | GRPC_INITIAL_METADATA_CORKED | \
-   GRPC_WRITE_THROUGH)
+#define GRPC_INITIAL_METADATA_USED_MASK                  \
+  (GRPC_INITIAL_METADATA_WAIT_FOR_READY_EXPLICITLY_SET | \
+   GRPC_INITIAL_METADATA_WAIT_FOR_READY | GRPC_WRITE_THROUGH)
 
 /** A single metadata element */
 typedef struct grpc_metadata {

include/grpcpp/impl/codegen/client_context.h

@@ -475,8 +475,7 @@ class ClientContext {
     return (wait_for_ready_ ? GRPC_INITIAL_METADATA_WAIT_FOR_READY : 0) |
            (wait_for_ready_explicitly_set_
                 ? GRPC_INITIAL_METADATA_WAIT_FOR_READY_EXPLICITLY_SET
-                : 0) |
-           (initial_metadata_corked_ ? GRPC_INITIAL_METADATA_CORKED : 0);
+                : 0);
   }
 
   std::string authority() { return authority_; }