tree-wide: Drop gnu-efi

This drops all mentions of gnu-efi and its manual build machinery. A
future commit will bring bootloader builds back. A new bootloader meson
option is now used to control whether to build sd-boot and its userspace
tooling.

shell-completion/bash/meson.build

@@ -31,7 +31,7 @@ items = [['busctl',              ''],
          ['systemd-path',        ''],
          ['systemd-run',         ''],
          ['udevadm',             ''],
-         ['bootctl',             'HAVE_GNU_EFI'],
+         ['bootctl',             'ENABLE_BOOTLOADER'],
          ['coredumpctl',         'ENABLE_COREDUMP'],
          ['homectl',             'ENABLE_HOMED'],
          ['hostnamectl',         'ENABLE_HOSTNAMED'],