Re: {heap,minimal}_expand_tuple() are unused

Hello PG hackers,

I saw this Commitfest patch and thought it might be a good one for me to
begin engaging with the PG community on through review. The patch removes
`expand_tuple, heap_expand_tuple, minimal_expand_tuple, and
heap_copytuple_with_tuple`.

I went ahead and checked out the PG master branch as of commit 6e70bef. I
verified the patch contents do what is expected -- removing these functions
and updating the test comments. I verified the patch applies cleanly to
6e70bef.

```
# On master
% git grep -n -w -e expand_tuple -e heap_expand_tuple -e
minimal_expand_tuple -e heap_copytuple_with_tuple master
master:src/backend/access/common/heaptuple.c:703: *
heap_copytuple_with_tuple
master:src/backend/access/common/heaptuple.c:712:heap_copytuple_with_tuple(HeapTuple
src, HeapTuple dest)
master:src/backend/access/common/heaptuple.c:738:expand_tuple(HeapTuple
*targetHeapTuple,
master:src/backend/access/common/heaptuple.c:962:minimal_expand_tuple(HeapTuple
sourceTuple, TupleDesc tupleDesc)
master:src/backend/access/common/heaptuple.c:966: expand_tuple(NULL,
&minimalTuple, sourceTuple, tupleDesc);
master:src/backend/access/common/heaptuple.c:974:heap_expand_tuple(HeapTuple
sourceTuple, TupleDesc tupleDesc)
master:src/backend/access/common/heaptuple.c:978:
expand_tuple(&heapTuple, NULL, sourceTuple, tupleDesc);
master:src/include/access/htup_details.h:809:extern void
heap_copytuple_with_tuple(HeapTuple src, HeapTuple dest);
master:src/include/access/htup_details.h:835:extern HeapTuple
heap_expand_tuple(HeapTuple sourceTuple, TupleDesc tupleDesc);
master:src/include/access/htup_details.h:836:extern MinimalTuple
minimal_expand_tuple(HeapTuple sourceTuple, TupleDesc tupleDesc);
master:src/test/regress/expected/fast_default.out:603:-- query to exercise
expand_tuple function
master:src/test/regress/expected/fast_default.out:639:-- in expand_tuple,
and that rows are correctly expanded for triggers
master:src/test/regress/sql/fast_default.sql:416:-- query to exercise
expand_tuple function
master:src/test/regress/sql/fast_default.sql:432:-- in expand_tuple, and
that rows are correctly expanded for triggers

# After the patch is applied
% git grep -n -w -e expand_tuple -e heap_expand_tuple -e
minimal_expand_tuple -e heap_copytuple_with_tuple review-7284
# Nothing found
```

Next I built Postgres in a Debian trixie-slim container (on ARM), with most
dependencies except docs and dtrace.

I ran a suite of tests with `meson test -C /build --print-errorlogs` which
passes.
```
Ok: 392
Expected Fail: 0
Fail: 0
Unexpected Pass: 0
Skipped: 36
Timeout: 0
```

All 36 skips are suites disabled by default: 35 gated behind PG_TEST_EXTRA,
which I did not set, plus one Windows-only SSPI authentication test.

I did not encounter any issues while evaluating the patch.

Best,
Kyle