efivars: kill SystemdOptions efi var support

This has been depracted since v254 (2023). Let's kill it for
good now, it has been long enough with 2y. Noone has shown up who wants
to keep it. And given it doesn't work in SB world anyway, and is not
measured is quite problematic security wise.

src/basic/proc-cmdline.h

@@ -9,8 +9,7 @@ typedef enum ProcCmdlineFlags {
         PROC_CMDLINE_STRIP_RD_PREFIX    = 1 << 0, /* automatically strip "rd." prefix if it is set (and we are in the initrd, since otherwise we'd not consider it anyway) */
         PROC_CMDLINE_VALUE_OPTIONAL     = 1 << 1, /* the value is optional (for boolean switches that can omit the value) */
         PROC_CMDLINE_RD_STRICT          = 1 << 2, /* ignore this in the initrd */
-        PROC_CMDLINE_IGNORE_EFI_OPTIONS = 1 << 3, /* don't check systemd's private EFI variable */
-        PROC_CMDLINE_TRUE_WHEN_MISSING  = 1 << 4, /* default to true when the key is missing for bool */
+        PROC_CMDLINE_TRUE_WHEN_MISSING  = 1 << 3, /* default to true when the key is missing for bool */
 } ProcCmdlineFlags;
 
 typedef int (*proc_cmdline_parse_t)(const char *key, const char *value, void *data);