meson: Drop legacy 'verify-signature' option

Currently there are two options for the image signature verification:
- 'verify-signature' (legacy),
- 'verify-full-signature' (current).

Drop legacy option and let the current one take its place.

Change-Id: Ia205424395179fd190e3d055159beca93cff0545
Signed-off-by: Konstantin Aladyshev <aladyshev22@gmail.com>
diff --git a/meson.build b/meson.build
index 7338236..e69e1ab 100644
--- a/meson.build
+++ b/meson.build
@@ -67,10 +67,7 @@
 
 # Configurable features
 conf.set('HOST_BIOS_UPGRADE', get_option('host-bios-upgrade').enabled())
-conf.set('WANT_SIGNATURE_VERIFY', \
-    get_option('verify-signature').enabled() or \
-    get_option('verify-full-signature').enabled())
-conf.set('WANT_SIGNATURE_FULL_VERIFY', get_option('verify-full-signature').enabled())
+conf.set('WANT_SIGNATURE_VERIFY', get_option('verify-signature').enabled())
 
 # Configurable variables
 conf.set('ACTIVE_BMC_MAX_ALLOWED', get_option('active-bmc-max-allowed'))