Don't set HAVE_SSP unconditionally on aarch64 (#43555)

There is no plausible reason for this. And indeed, this patch fixes
compilation for the libjulia_jll builder on Yggdrasil which currently fails
due to the absence of libssp.

The removed line was introduced in PR #41936 but without any justification
that I could discern, so it might have just slipped in there accidentally.

Author: fingolfin

Make.inc

@@ -891,7 +891,6 @@ OPENBLAS_DYNAMIC_ARCH:=0
 OPENBLAS_TARGET_ARCH:=ARMV8
 USE_BLAS64:=1
 BINARY:=64
-HAVE_SSP:=1
 ifeq ($(OS),Darwin)
 # Apple Chips are all at least A12Z
 MCPU:=apple-a12