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/dbus-unit.c

@@ -32,7 +32,7 @@
 #include "special.h"
 #include "string-util.h"
 #include "strv.h"
-#include "transaction.h"
+#include "transaction.h"                /* IWYU pragma: keep */
 #include "unit-name.h"
 #include "web-util.h"