clang-tidy: Fix all remaining misc-include-cleaner violations

- Remove unused includes
- Add common false positive headers to misc-include-cleaner.IgnoreHeaders
- Add IWYU pragma keep for uncommon false positive headers

src/core/unit.c

@@ -11,7 +11,6 @@
 #include "all-units.h"
 #include "alloc-util.h"
 #include "ansi-color.h"
-#include "bpf-firewall.h"
 #include "bpf-restrict-fs.h"
 #include "bus-common-errors.h"
 #include "bus-internal.h"