Remove unsupported cpu attribute from cc_toolchains.

Fixes bazelbuild#8236

Issue bazelbuild#7075

RELNOTES: None.
PiperOrigin-RevId: 247014090

tools/cpp/BUILD

@@ -115,7 +115,6 @@ cc_toolchain(
     ar_files = ":empty",
     as_files = ":empty",
     compiler_files = ":empty",
-    cpu = "local",
     dwp_files = ":empty",
     linker_files = ":empty",
     objcopy_files = ":empty",
@@ -147,7 +146,6 @@ cc_toolchain(
     ar_files = ":empty",
     as_files = ":empty",
     compiler_files = ":empty",
-    cpu = "ppc",
     dwp_files = ":empty",
     linker_files = ":empty",
     objcopy_files = ":empty",
@@ -175,7 +173,6 @@ cc_toolchain(
     ar_files = ":empty",
     as_files = ":empty",
     compiler_files = ":empty",
-    cpu = "s390x",
     dwp_files = ":empty",
     linker_files = ":empty",
     objcopy_files = ":empty",
@@ -203,7 +200,6 @@ cc_toolchain(
     ar_files = ":empty",
     as_files = ":empty",
     compiler_files = ":empty",
-    cpu = "local",
     dwp_files = ":empty",
     linker_files = ":empty",
     objcopy_files = ":empty",
@@ -231,7 +227,6 @@ cc_toolchain(
     ar_files = ":empty",
     as_files = ":empty",
     compiler_files = ":empty",
-    cpu = "local",
     dwp_files = ":empty",
     linker_files = ":empty",
     objcopy_files = ":empty",
@@ -261,7 +256,6 @@ cc_toolchain(
     ar_files = ":empty",
     as_files = ":empty",
     compiler_files = ":osx_wrapper",
-    cpu = "darwin",
     dwp_files = ":empty",
     linker_files = ":osx_wrapper",
     objcopy_files = ":empty",
@@ -297,7 +291,6 @@ cc_toolchain(
     ar_files = ":empty",
     as_files = ":empty",
     compiler_files = ":empty",
-    cpu = "local",
     dwp_files = ":empty",
     linker_files = ":empty",
     objcopy_files = ":empty",
@@ -333,7 +326,6 @@ cc_toolchain(
     ar_files = ":empty",
     as_files = ":empty",
     compiler_files = ":empty",
-    cpu = "local",
     dwp_files = ":empty",
     linker_files = ":empty",
     objcopy_files = ":empty",
@@ -369,7 +361,6 @@ cc_toolchain(
     ar_files = ":empty",
     as_files = ":empty",
     compiler_files = ":compile-x64_windows",
-    cpu = "x64_windows",
     dwp_files = ":empty",
     linker_files = ":empty",
     objcopy_files = ":empty",