Cleanup: move clear_table() to divesite.c

There were two declaration of clear_table(), one in dive.h and one
in parse.h. The definition was in parse.c. Since the parser doesn't
even use the function, move the function and its declaration to
divelist.[ch] and remove the redundant declaration in dive.h.

Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>

core/divelist.h

@@ -58,6 +58,7 @@ void reset_min_datafile_version();
 void report_datafile_version(int version);
 int get_dive_id_closest_to(timestamp_t when);
 void clear_dive_file_data();
+void clear_table(struct dive_table *table);
 
 #ifdef DEBUG_TRIP
 extern void dump_selection(void);