Consolidation with CDI-PIO (develop)

Generally, this is !11 (merged) rebased onto the develop branch.

This is the first develop-based version accepted by the Buildbot of ICON: https://buildbot.dkrz.de/grid?branch=m300488/cdi-pio-2-integration

src/pio_dbuffer.c

@@ -72,12 +72,6 @@ dbuffer_cleanup(struct dBuffer **dbuffer)
   return;
 }
 
-size_t
-dbuffer_data_size(struct dBuffer *dbuffer)
-{
-  return dbuffer->wr_pointer;
-}
-
 static size_t
 dbuffer_freesize(struct dBuffer *dbuffer)
 {
@@ -85,13 +79,6 @@ dbuffer_freesize(struct dBuffer *dbuffer)
   return free_size;
 }
 
-int
-dbuffer_reset(struct dBuffer *dbuffer)
-{
-  dbuffer->wr_pointer = 0;
-  return 0;
-}
-
 int
 dbuffer_push(struct dBuffer *dbuffer, const void *buffer, size_t len)
 {