Remove unused variables in gloo/rendezvous/redis_store.cc

Summary:
LLVM-15 has a warning `-Wunused-but-set-variable` which we treat as an error because it's so often diagnostic of a code issue. Unused variables can compromise readability or, worse, performance.

This diff either (a) removes an unused variable and, possibly, it's associated code, or (b) qualifies the variable with `[[maybe_unused]]`, mostly in cases where the variable _is_ used, but, eg, in an `assert` statement that isn't present in production code.

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Reviewed By: danzimm

Differential Revision: D52848007

fbshipit-source-id: 58693326dda966d9496635ef292e3a768ea26672

gloo/rendezvous/redis_store.cc

@@ -17,8 +17,6 @@
 namespace gloo {
 namespace rendezvous {
 
-static const std::chrono::seconds kWaitTimeout = std::chrono::seconds(60);
-
 RedisStore::RedisStore(const std::string& host, int port) {
   struct timeval timeout = {.tv_sec = 2};
   redis_ = redisConnectWithTimeout(host.c_str(), port, timeout);