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/fundamental/iovec-util-fundamental.h

@@ -5,7 +5,7 @@
 #include <sys/uio.h>
 #endif
 
-#include "assert-fundamental.h"
+#include "assert-fundamental.h"         /* IWYU pragma: keep */
 #include "macro-fundamental.h"
 
 #if SD_BOOT

src/fundamental/sha1-fundamental.c

@@ -77,7 +77,7 @@ modified for use with systemd
 */
 
 #if SD_BOOT
-#  include "efi-string.h"
+#  include "efi-string.h"       /* IWYU pragma: keep */
 #else
 #  include <string.h>
 #endif

src/fundamental/sha256-fundamental.c

@@ -22,7 +22,7 @@
    <https://www.gnu.org/licenses/>.  */
 
 #if SD_BOOT
-#  include "efi-string.h"
+#  include "efi-string.h"       /* IWYU pragma: keep */
 #else
 #  include <string.h>
 #endif

src/fundamental/string-util-fundamental.h

@@ -8,7 +8,7 @@
 #  include <string.h>
 #endif
 
-#include "assert-fundamental.h"
+#include "assert-fundamental.h"         /* IWYU pragma: keep */
 #include "macro-fundamental.h"
 
 /* What is interpreted as whitespace? */