fix some lint warnings

This fixes some of the IWYU and cppcheck lint warnings. And only on
macOS (formerly OS X). Fixing these types of warnings on a broader set
of platforms should be done but this is a baby step to making `make
lint-all` have few, if any, warnings. This reduces the number of lines
in the `make lint-all` output on macOS by over 500 lines.

src/autoload.cpp

@@ -1,7 +1,6 @@
 // The classes responsible for autoloading functions and completions.
 #include "config.h"  // IWYU pragma: keep
 
-#include <assert.h>
 #include <errno.h>
 #include <pthread.h>
 #include <stddef.h>