Fix some compiler warnings

.../src/scitokens_internal.h:673:25: warning: moving a local object in a return statement prevents copy elision [-Wpessimizing-move]
  673 |         return std::move(result);
      |                ~~~~~~~~~^~~~~~~~
.../src/scitokens_internal.h:673:25: note: remove 'std::move' call

.../src/scitokens_internal.cpp:633:25: warning: moving a local object in a return statement prevents copy elision [-Wpessimizing-move]
  633 |         return std::move(status);
      |                ~~~~~~~~~^~~~~~~~
.../src/scitokens_internal.cpp:633:25: note: remove 'std::move' call

.../src/scitokens_internal.cpp:747:13: warning: unused variable 'next_update' [-Wunused-variable]
  747 |     int64_t next_update, expires;
      |             ^~~~~~~~~~~

.../src/scitokens_internal.cpp:747:26: warning: unused variable 'expires' [-Wunused-variable]
  747 |     int64_t next_update, expires;
      |                          ^~~~~~~

.../test/main.cpp:442:12: warning: unused variable 'now' [-Wunused-variable]
  442 |     time_t now = time(NULL);
      |            ^~~

Author: ellert

src/scitokens_internal.cpp

@@ -630,7 +630,7 @@ Validator::get_public_keys_from_web(const std::string &issuer,
     auto cget_status = status->m_cget->perform_start(openid_metadata);
     status->m_continue_fetch = true;
     if (!cget_status.m_done) {
-        return std::move(status);
+        return status;
     }
     return get_public_keys_from_web_continue(std::move(status));
 }
@@ -744,7 +744,6 @@ std::string Validator::get_jwks(const std::string &issuer) {
 }
 
 bool Validator::refresh_jwks(const std::string &issuer) {
-    int64_t next_update, expires;
     picojson::value keys;
     std::unique_ptr<scitokens::AsyncStatus> status = get_public_keys_from_web(
         issuer, internal::SimpleCurlGet::extended_timeout);

src/scitokens_internal.h

@@ -670,7 +670,7 @@ class Validator {
         }
         std::unique_ptr<AsyncStatus> result(new AsyncStatus());
         result->m_done = true;
-        return std::move(result);
+        return result;
     }
 
     void add_critical_claims(const std::vector<std::string> &claims) {

test/main.cpp

@@ -439,7 +439,6 @@ TEST_F(SerializeTest, FailDeserializeAsyncTest) {
 }
 
 TEST_F(SerializeTest, ExplicitTime) {
-    time_t now = time(NULL);
     char *err_msg = nullptr;
 
     scitoken_set_serialize_profile(m_token.get(), SciTokenProfile::WLCG_1_0);