spdlog: do not drop logger in destructor

For static objects, the order of destruction is in reverse of the order
of construction, but the latter is hard to control except among static
objects defined within the same translation unit. This means that spdlog
may be destructed before spdlog::drop() is invoked in the destructor,
which leads to a segmentation fault due to memory use-after-free.

The spdlog example points out that dropping all loggers via
spdlog::shutdown(), which invokes spdlog::drop_all(), is optional.

Omit destructor calls of spdlog::drop(), but retain non-destructor calls
of spdlog::drop_all() for now since they do not cause any harm.

Link: ros2/rclcpp#933
Link: gabime/spdlog#1738
Link: https://github.com/gabime/spdlog/blob/a2b4262090fd3f005c2315dcb5be2f0f1774a005/example/example.cpp#L96
Closes: https://hsdes.intel.com/appstore/article/#/22019839238
Signed-off-by: Peter Colberg <peter.colberg@intel.com>

libraries/afu-test/afu_test.h

@@ -186,8 +186,6 @@ class afu {
     app_.add_option("-t,--timeout", timeout_msec_, "test timeout (msec)")->default_str(std::to_string(timeout_msec_));
   }
   virtual ~afu() {
-    if (logger_)
-      spdlog::drop(logger_->name());
   }
 
   CLI::App & cli() { return app_; }

samples/cxl_hello_fpga/he_cache_test.h

@@ -297,7 +297,6 @@ class afu {
   }
   virtual ~afu() {
     if (fd_ > 0) close(fd_);
-    if (logger_) spdlog::drop(logger_->name());
   }
 
   CLI::App &cli() { return app_; }

samples/cxl_host_exerciser/he_cache_test.h

@@ -304,8 +304,6 @@ class afu {
 
     if (fd_ > 0)
         close(fd_);
-    if (logger_)
-      spdlog::drop(logger_->name());
   }
 
   CLI::App &cli() { return app_; }