Disable the AVX512 DGEMM kernel (again)

Due to as yet unresolved errors seen in #1955 and #2029

Author: martin-frbg

kernel/x86_64/KERNEL.SKYLAKEX

@@ -7,7 +7,7 @@ SGEMMITCOPY    =  sgemm_tcopy_16_skylakex.c
 SGEMMONCOPY    =  sgemm_ncopy_4_skylakex.c
 SGEMMOTCOPY    =  ../generic/gemm_tcopy_4.c
 
-DGEMMKERNEL    =  dgemm_kernel_4x8_skylakex.c
+#DGEMMKERNEL    =  dgemm_kernel_4x8_skylakex.c
 
 DGEMMINCOPY    =  dgemm_ncopy_8_skylakex.c
 DGEMMITCOPY    =  dgemm_tcopy_8_skylakex.c