trace: drop unused TraceBufferRecord->next_tbuf_idx field

Signed-off-by: Harsh Prateek Bora <harsh@linux.vnet.ibm.com>
Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>

trace/simple.c

@@ -231,8 +231,6 @@ int trace_record_start(TraceBufferRecord *rec, TraceEventID event, size_t datasi
     }
 
     idx = old_idx % TRACE_BUF_LEN;
-    /*  To check later if threshold crossed */
-    rec->next_tbuf_idx = new_idx % TRACE_BUF_LEN;
 
     rec_off = idx;
     rec_off = write_to_buffer(rec_off, &event, sizeof(event));

trace/simple.h

@@ -29,7 +29,6 @@ void st_flush_trace_buffer(void);
 
 typedef struct {
     unsigned int tbuf_idx;
-    unsigned int next_tbuf_idx;
     unsigned int rec_off;
 } TraceBufferRecord;