EDAC/thunderx: Remove unused struct error_syndrome

struct error_syndrome appears never to have been used. Remove it,
together with the MAX_SYNDROME_REGS it used.

Signed-off-by: Dr. David Alan Gilbert <linux@treblig.org>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20240516133404.251397-1-linux@treblig.org