message: Remove libevent and leveldb submodules
diff: path = external/openssl-cmake
  url = https://github.com/spectrecoin/openssl-cmake.git
  branch = spectrecoin_openssl_1.1.0l
  -[submodule "external/libevent"]
  - path = external/libevent
  - url = https://github.com/libevent/libevent.git
  - branch = master
  -[submodule "external/leveldb"]
  - path = external/leveldb
  - url = https://github.com/google/leveldb.git
  - branch = master
  