Remove duplicate lines of code

Commit 6df7a9698b accidentally included two identical prototypes for
default_multirange_selectivi() and commit 086cf1458c added a break;
statement where one was already present, thus duplicating it.  While
there is no bug caused by this, fix by removing the duplicated lines
as they provide no value.

Backpatch the fix for duplicate prototypes to v14 and the duplicate
break statement fix to all supported branches to avoid backpatching
hazards due to the removal.

Reported-by: Anton Voloshin <a.voloshin@postgrespro.ru>
Discussion: https://postgr.es/m/0e69cb60-0176-f6d0-7e15-6478b7d85724@postgrespro.ru

src/backend/utils/adt/multirangetypes_selfuncs.c

@@ -35,7 +35,6 @@ static double calc_multirangesel(TypeCacheEntry *typcache,
 								 VariableStatData *vardata,
 								 const MultirangeType *constval, Oid operator);
 static double default_multirange_selectivity(Oid operator);
-static double default_multirange_selectivity(Oid operator);
 static double calc_hist_selectivity(TypeCacheEntry *typcache,
 									VariableStatData *vardata,
 									const MultirangeType *constval,

src/interfaces/ecpg/preproc/variable.c

@@ -105,7 +105,6 @@ find_struct_member(char *name, char *str, struct ECPGstruct_member *members, int
 						else
 							return find_struct_member(name, ++end, members->type->u.members, brace_level);
 						break;
-						break;
 					case '.':
 						if (members->type->type == ECPGt_array)
 							return find_struct_member(name, end, members->type->u.element->u.members, brace_level);