Remove an unneeded variable.

Found using Clang's static analyzer.
diff --git a/Objects/obmalloc.c b/Objects/obmalloc.c
index fa985da..c8c36d5 100644
--- a/Objects/obmalloc.c
+++ b/Objects/obmalloc.c
@@ -1761,7 +1761,6 @@
 	 * will be living in full pools -- would be a shame to miss them.
 	 */
 	for (i = 0; i < maxarenas; ++i) {
-		uint poolsinarena;
 		uint j;
 		uptr base = arenas[i].address;
 
@@ -1770,7 +1769,6 @@
 			continue;
 		narenas += 1;
 
-		poolsinarena = arenas[i].ntotalpools;
 		numfreepools += arenas[i].nfreepools;
 
 		/* round up to pool alignment */