Remove .mk references to unused p9a object files

Fixes build fail for mirrored ekb/master commit
https://rchgit01.rchland.ibm.com/gerrit1/#/c/96166/.
Changes to the makefile of this commit helps the
referenced gerrit commit pass Jenkins CI.

Change-Id: I7b3767503a4ef1591b9c6eda3b02fb44bf883d1a
Reviewed-on: http://rchgit01.rchland.ibm.com/gerrit1/96204
Tested-by: Jenkins Server <pfd-jenkins+hostboot@us.ibm.com>
Tested-by: Jenkins OP Build CI <op-jenkins+hostboot@us.ibm.com>
Tested-by: FSP CI Jenkins <fsp-CI-jenkins+hostboot@us.ibm.com>
Tested-by: Jenkins OP HW <op-hw-jenkins+hostboot@us.ibm.com>
Reviewed-by: Daniel M Crowell <dcrowell@us.ibm.com>

src/usr/isteps/mss/runtime/makefile

@@ -83,14 +83,12 @@ VPATH += ${MSS_LIB}
 #######
 # Add the specific files we need for HBRT
 OBJS += c_str.o
-OBJS += axone_c_str.o
 OBJS += nimbus_c_str.o
 OBJS += mcbist.o
 OBJS += mcbist_workarounds.o
 OBJS += rank.o
 OBJS += memory_size.o
 OBJS += gen_mss_mcbist_patterns.o
-OBJS += axone_pos.o
 OBJS += nimbus_pos.o
 OBJS += unmask.o