Remove last traces of previously deleted bgzf_idx_amend_last()

As noted in #1722, this function was removed in PR #1672.

Author: jmarshall

hts_internal.h

@@ -123,18 +123,6 @@ const char *hts_plugin_path(void);
  */
 int bgzf_idx_push(BGZF *fp, hts_idx_t *hidx, int tid, hts_pos_t beg, hts_pos_t end, uint64_t offset, int is_mapped);
 
-/*
- * bgzf analogue to hts_idx_amend_last.
- *
- * This is needed when multi-threading and writing indices on the fly.
- * At the point of writing a record we know the virtual offset for start
- * and end, but that end virtual offset may be the end of the current
- * block.  In standard indexing our end virtual offset becomes the start
- * of the next block.  Thus to ensure bit for bit compatibility we
- * detect this boundary case and fix it up here.
- */
-void bgzf_idx_amend_last(BGZF *fp, hts_idx_t *hidx, uint64_t offset);
-
 static inline int find_file_extension(const char *fn, char ext_out[static HTS_MAX_EXT_LEN])
 {
     const char *delim = fn ? strstr(fn, HTS_IDX_DELIM) : NULL, *ext;