xdiff: remove unused data from xdlclass_t

Prior to commit 6d507bd (xdiff: delete fields ha, line, size
in xdlclass_t in favor of an xrecord_t, 2025-09-26) xdlclass_t
carried a copy of all the fields in xrecord_t. That commit embedded
xrecord_t in xdlclass_t to make it easier to change the types of
the fields in xrecord_t. However commit 6a26019 (xdiff: split
xrecord_t.ha into line_hash and minimal_perfect_hash, 2025-11-18)
added the "minimal_perfect_hash" field to xrecord_t which is not
used by xdlclass_t. To avoid wasting space stop copying the whole
of xrecord_t and just copy the pointer and length that we need to
intern the line. Together with the previous commit this effectively
reverts 6d507bd.

Signed-off-by: Phillip Wood <phillip.wood@dunelm.org.uk>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: phillipwood

xdiff/xprepare.c

@@ -36,7 +36,8 @@
 typedef struct s_xdlclass {
 	uint64_t line_hash;
 	struct s_xdlclass *next;
-	xrecord_t rec;
+	const uint8_t *ptr;
+	size_t size;
 	long idx;
 	long len1, len2;
 } xdlclass_t;
@@ -101,7 +102,7 @@ static int xdl_classify_record(unsigned int pass, xdlclassifier_t *cf, xrecord_t
 	hi = XDL_HASHLONG(line_hash, cf->hbits);
 	for (rcrec = cf->rchash[hi]; rcrec; rcrec = rcrec->next)
 		if (rcrec->line_hash == line_hash &&
-				xdl_recmatch((const char *)rcrec->rec.ptr, (long)rcrec->rec.size,
+				xdl_recmatch((const char *)rcrec->ptr, (long)rcrec->size,
 					(const char *)rec->ptr, (long)rec->size, cf->flags))
 			break;
 
@@ -115,7 +116,8 @@ static int xdl_classify_record(unsigned int pass, xdlclassifier_t *cf, xrecord_t
 				return -1;
 		cf->rcrecs[rcrec->idx] = rcrec;
 		rcrec->line_hash = line_hash;
-		rcrec->rec = *rec;
+		rcrec->ptr = rec->ptr;
+		rcrec->size = rec->size;
 		rcrec->len1 = rcrec->len2 = 0;
 		rcrec->next = cf->rchash[hi];
 		cf->rchash[hi] = rcrec;