meta-ibm: p10bmc: Clean up variable definitions

With the reshuffle that occurred in 38cfcc393d9e ("meta-aspeed:
u-boot-aspeed-sdk: Use provided signing key by default") we no-longer
need to specify these options in p10bmc.conf

Mistakenly, `SOCSEC_SIGN_ENABLE = "1"` was duplicated later in the file
by 699146128388 ("meta-ibm: p10bmc: Assert that we want the SPL signed
by socsec"). Removing the instance as done in this patch still leaves us
with the positive assertion that we want SPL signing enabled.

Change-Id: Iaa9cbe5b0ba4aaf69bb0fba1eb8f6bc62d085a33
Signed-off-by: Andrew Jeffery <andrew@aj.id.au>
diff --git a/meta-ibm/conf/machine/p10bmc.conf b/meta-ibm/conf/machine/p10bmc.conf
index 19de5ee..4956f87 100644
--- a/meta-ibm/conf/machine/p10bmc.conf
+++ b/meta-ibm/conf/machine/p10bmc.conf
@@ -37,9 +37,6 @@
 
 UBOOT_SIGN_ENABLE = "1"
 SPL_SIGN_ENABLE = "1"
-SOCSEC_SIGN_ENABLE = "1"
-SOCSEC_SIGN_EXTRA_OPTS = "--stack_intersects_verification_region=false"
-SOCSEC_SIGN_KEY ?= "${WORKDIR}/rsa_oem_dss_key.pem"
 
 FIT_HASH_ALG = "sha512"
 FIT_SIGN_ALG = "rsa4096"