Osx: Do not use CROSSTOOL to select cc_toolchain

This is a preparation for flipping
--incompatible_disable_cc_toolchain_label_from_crosstool_proto, which will stop
reading default_toolchain fields from the crosstool and will rely on
cc_toolchain_suite.toolchains containing entries for cpu without compiler.

RELNOTES: None.
PiperOrigin-RevId: 216717701

tools/osx/crosstool/CROSSTOOL.tpl

@@ -6,55 +6,6 @@
 
 major_version: "1"
 minor_version: "0"
-default_target_cpu: "same_as_host"
-default_toolchain {
-  cpu: "darwin"
-  toolchain_identifier: "darwin_x86_64"
-}
-default_toolchain {
-  cpu: "darwin_x86_64"
-  toolchain_identifier: "darwin_x86_64"
-}
-default_toolchain {
-  cpu: "k8"
-  toolchain_identifier: "darwin_x86_64"
-}
-default_toolchain {
-  cpu: "ios_x86_64"
-  toolchain_identifier: "ios_x86_64"
-}
-default_toolchain {
-  cpu: "ios_i386"
-  toolchain_identifier: "ios_i386"
-}
-default_toolchain {
-  cpu: "ios_armv7"
-  toolchain_identifier: "ios_armv7"
-}
-default_toolchain {
-  cpu: "ios_arm64"
-  toolchain_identifier: "ios_arm64"
-}
-default_toolchain {
-  cpu: "watchos_i386"
-  toolchain_identifier: "watchos_i386"
-}
-default_toolchain {
-  cpu: "watchos_armv7k"
-  toolchain_identifier: "watchos_armv7k"
-}
-default_toolchain {
-  cpu: "tvos_x86_64"
-  toolchain_identifier: "tvos_x86_64"
-}
-default_toolchain {
-  cpu: "tvos_arm64"
-  toolchain_identifier: "tvos_arm64"
-}
-default_toolchain {
-  cpu: "armeabi-v7a"
-  toolchain_identifier: "stub_armeabi-v7a"
-}
 toolchain {
   toolchain_identifier: "darwin_x86_64"
 %{cxx_builtin_include_directory}