Remove RPC support for the efr32 lock app

[andy31415]

Problem

Lock app does not support RPC (compilation fails):

2021-10-05 15:59:42 INFO    /home/vscode/pigweed/env/cipd/pigweed/bin/../lib/gcc/arm-none-eabi/10.2.1/../../../../arm-none-eabi/bin/ld: obj/third_party/connectedhomeip/third_party/pigweed/repo/pw_kvs/pw_kvs.entry.cc.o: in function `pw::kvs::internal::Entry::Read(pw::kvs::FlashPartition&, unsigned long, pw::kvs::internal::EntryFormats const&, pw::kvs::internal::Entry*)':
2021-10-05 15:59:42 INFO    out/third_party/connectedhomeip/third_party/pigweed/repo/pw_kvs/entry.cc:54: undefined reference to `pw_Log'
2021-10-05 15:59:42 INFO    /home/vscode/pigweed/env/cipd/pigweed/bin/../lib/gcc/arm-none-eabi/10.2.1/../../../../arm-none-eabi/bin/ld: obj/third_party/connectedhomeip/third_party/pigweed/repo/pw_kvs/pw_kvs.entry.cc.o: in function `pw::kvs::internal::Entry::VerifyChecksumInFlash() const':
2021-10-05 15:59:42 INFO    out/third_party/connectedhomeip/third_party/pigweed/repo/pw_kvs/entry.cc:214: undefined reference to `pw_Log'
2021-10-05 15:59:42 INFO    /home/vscode/pigweed/env/cipd/pigweed/bin/../lib/gcc/arm-none-eabi/10.2.1/../../../../arm-none-eabi/bin/ld: obj/third_party/connectedhomeip/third_party/pigweed/repo/pw_kvs/pw_kvs.entry_cache.cc.o: in function `pw::kvs::internal::EntryCache::Find(pw::kvs::FlashPartition&, pw::kvs::internal::Sectors const&, pw::kvs::internal::EntryFormats const&, pw::kvs::Key, pw::kvs::internal::EntryMetadata*) const':
2021-10-05 15:59:42 INFO    out/third_party/connectedhomeip/third_party/pigweed/repo/pw_kvs/entry_cache.cc:96: undefined reference to `pw_Log'
2021-10-05 15:59:42 INFO    /home/vscode/pigweed/env/cipd/pigweed/bin/../lib/gcc/arm-none-eabi/10.2.1/../../../../arm-none-eabi/bin/ld: out/third_party/connectedhomeip/third_party/pigweed/repo/pw_kvs/entry_cache.cc:105: undefined reference to `pw_Log'
2021-10-05 15:59:42 INFO    /home/vscode/pigweed/env/cipd/pigweed/bin/../lib/gcc/arm-none-eabi/10.2.1/../../../../arm-none-eabi/bin/ld: out/third_party/connectedhomeip/third_party/pigweed/repo/pw_kvs/entry_cache.cc:112: undefined reference to `pw_Log'
2021-10-05 15:59:42 INFO    /home/vscode/pigweed/env/cipd/pigweed/bin/../lib/gcc/arm-none-eabi/10.2.1/../../../../arm-none-eabi/bin/ld: obj/third_party/connectedhomeip/third_party/pigweed/repo/pw_kvs/pw_kvs.entry_cache.cc.o:out/third_party/connectedhomeip/third_party/pigweed/repo/pw_kvs/entry_cache.cc:159: more undefined references to `pw_Log' follow
2021-10-05 15:59:42 INFO    collect2: error: ld returned 1 exit status
2021-10-05 15:59:42 INFO    ninja: build stopped: subcommand failed.

Change overview

Remove -rpc variant from efr32-lock

Testing

unit test shows variant was removed

[andy31415]

Hotfix: github CI is broken and cannot validate this in general. CI that builds -rpc variant is in cloudbuild.