Stop calling xmlMemoryDump

This was used to check for memory leaks but could potentially create a
.memdump file. These days, there are better ways to check for memory
leaks.

python/tests/xpathleak.py

@@ -51,5 +51,3 @@ if leakedbytes == 0:
 	print("OK")
 else:
 	print("Memory leak", leakedbytes, "bytes")
-	# drop file to .memdump file in cwd, but won't work if not compiled in
-	libxml2.dumpMemory()