Ignore jemalloc versions before 4.0.0

We now depend on explicitly creating memory arenas and disabling tcache
on those, and these features are not available with jemalloc < 4.
Instead of working around these issues, make the jemalloc >= 4.0.0 hard
requirement by looking for sdallocx() symbol that's only available from
that version.

The jemalloc < 4 was only used by RHEL 7 which is not supported since
BIND 9.19+.

lib/isc/mem.c

@@ -52,11 +52,6 @@
 #elif defined(HAVE_JEMALLOC)
 #include <jemalloc/jemalloc.h>
 #define JEMALLOC_API_SUPPORTED 1
-
-#if JEMALLOC_VERSION_MAJOR < 4
-#define sdallocx(ptr, size, flags) dallocx(ptr, flags)
-#endif /* JEMALLOC_VERSION_MAJOR < 4 */
-
 #else
 #include "jemalloc_shim.h"
 #endif