Revert "src/cpu,soc/amd/common/block/cpu: Add preload_microcode"

This reverts commit 4b5a490b6f.

Reason for revert: This effort was apparently given up on since 4 years.
So remove the function, since it is not used at the moment. If someone
wants to bring that effort back to live, said person can feel free to do
so.

Change-Id: I26d5c9fbfd6eae24f876d857a6e952ca0d1a64ae
Signed-off-by: Maximilian Brune <maximilian.brune@9elements.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/87066
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Matt DeVillier <matt.devillier@gmail.com>

src/include/cpu/amd/microcode.h

@@ -7,6 +7,5 @@ void amd_update_microcode_from_cbfs(void);
 void amd_load_microcode_from_cbfs(void);
 void amd_free_microcode(void);
 void amd_apply_microcode_patch(void);
-void preload_microcode(void);
 
 #endif /* CPU_AMD_MICROCODE_H */