tools: PCI: Remove unused BILLION macro

The macro BILLION is never referenced in the code.  Remove it.

Link: https://lore.kernel.org/r/20240911060401.9230-1-zhangjiao2@cmss.chinamobile.comSigned-off-by: zhang jiao <zhangjiao2@cmss.chinamobile.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Signed-off-by: Krzysztof Wilczyński <kwilczynski@kernel.org>

tools/pci/pcitest.c

@@ -16,8 +16,6 @@
 
 #include <linux/pcitest.h>
 
-#define BILLION 1E9
-
 static char *result[] = { "NOT OKAY", "OKAY" };
 static char *irq[] = { "LEGACY", "MSI", "MSI-X" };