intel/quark/storage_test.h: Drop external variable declaration

These are only used where they are initially declared.

Change-Id: I0a81a945b771b6c29a170c479b9e72c98e8f3c5a
Signed-off-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/33022
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Patrick Georgi <pgeorgi@google.com>

src/soc/intel/quark/include/soc/storage_test.h

@@ -48,9 +48,4 @@ struct log_entry {
 
 #define LOG_ENTRIES	256
 
-extern struct log_entry log[LOG_ENTRIES];
-extern uint8_t log_index;
-extern int log_full;
-extern long log_start_time;
-
 #endif /* __STORAGE_TEST_H__ */