soc/amd/commonn/block/include/psp_efs.h: Remove unused function

Commit 49d8aa7043ea ("soc/amd/common/block/psp: Unmap EFS region after
use") removed the 'efs_is_valid' function but left the function
signature in the header file.

TEST=stoney/picasso/cezanne/mendocino/phoenix builds

Signed-off-by: Fred Reitberger <reitbergerfred@gmail.com>
Change-Id: Ib596946679b50be63868af57e3428b4d65845419
Reviewed-on: https://review.coreboot.org/c/coreboot/+/76750
Reviewed-by: Matt DeVillier <matt.devillier@amd.corp-partner.google.com>
Reviewed-by: Felix Held <felix-coreboot@felixheld.de>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Eric Lai <eric_lai@quanta.corp-partner.google.com>
diff --git a/src/soc/amd/common/block/include/amdblocks/psp_efs.h b/src/soc/amd/common/block/include/amdblocks/psp_efs.h
index 1f87b85..1608ce5 100644
--- a/src/soc/amd/common/block/include/amdblocks/psp_efs.h
+++ b/src/soc/amd/common/block/include/amdblocks/psp_efs.h
@@ -61,7 +61,6 @@
 	uint32_t reserved_4Ch;
 } __attribute__((packed, aligned(16)));
 
-bool efs_is_valid(void);
 bool read_efs_spi_settings(uint8_t *mode, uint8_t *speed);
 
 #endif  /* AMD_COMMON_PSP_EFS_H */