Condense duplicate settings of --extra_execution_platforms into a single comma-separated list in anticipation of making --extra_execution_platform support overwrites.

This should be a no-op

PiperOrigin-RevId: 515650981
Change-Id: I6ade2e35969ed2300b7ab5dc2c9905e8dd764752
diff --git a/.bazelrc b/.bazelrc
index 6ee970b..74accc5 100644
--- a/.bazelrc
+++ b/.bazelrc
@@ -16,8 +16,7 @@
 build:ubuntu1804_java11 --extra_toolchains=@rbe_ubuntu1804_java11//java:all
 build:ubuntu1804_java11 --crosstool_top=@rbe_ubuntu1804_java11//cc:toolchain
 build:ubuntu1804_java11 --extra_toolchains=@rbe_ubuntu1804_java11//config:cc-toolchain
-build:ubuntu1804_java11 --extra_execution_platforms=//:rbe_ubuntu1804_java11_platform
-build:ubuntu1804_java11 --extra_execution_platforms=//:rbe_ubuntu1804_java11_highcpu_platform
+build:ubuntu1804_java11 --extra_execution_platforms=//:rbe_ubuntu1804_java11_platform,//:rbe_ubuntu1804_java11_highcpu_platform
 build:ubuntu1804_java11 --host_platform=//:rbe_ubuntu1804_java11_platform
 build:ubuntu1804_java11 --platforms=//:rbe_ubuntu1804_java11_platform
 build:ubuntu1804_java11 --config=remote_shared