PPC/s390: remove code-stubs related build files

R=jgruber@chromium.org, joransiu@ca.ibm.com

Change-Id: If31804509eaca51c0606409873dc180df4fb49f3
Reviewed-on: https://chromium-review.googlesource.com/c/1393301Reviewed-by: Joran Siu <joransiu@ca.ibm.com>
Reviewed-by: Sigurd Schneider <sigurds@chromium.org>
Commit-Queue: Junliang Yan <jyan@ca.ibm.com>
Cr-Commit-Position: refs/heads/master@{#58528}

BUILD.gn

@@ -2992,7 +2992,6 @@ v8_source_set("v8_base") {
       "src/ppc/assembler-ppc-inl.h",
       "src/ppc/assembler-ppc.cc",
       "src/ppc/assembler-ppc.h",
-      "src/ppc/code-stubs-ppc.cc",
       "src/ppc/codegen-ppc.cc",
       "src/ppc/constants-ppc.cc",
       "src/ppc/constants-ppc.h",
@@ -3023,7 +3022,6 @@ v8_source_set("v8_base") {
       "src/s390/assembler-s390-inl.h",
       "src/s390/assembler-s390.cc",
       "src/s390/assembler-s390.h",
-      "src/s390/code-stubs-s390.cc",
       "src/s390/codegen-s390.cc",
       "src/s390/constants-s390.cc",
       "src/s390/constants-s390.h",