Remove check for the 'verify-full-signature' option

'verify-full-signature' option is a legacy option that was recently
dropped from the build configuration. Therefore the build system
shouldn't check it.

Change-Id: I3a8be29991bd50d074fcfd6aa9d61a8777e5694e
Signed-off-by: Konstantin Aladyshev <aladyshev22@gmail.com>
diff --git a/meson.build b/meson.build
index e69e1ab..5e3e630 100644
--- a/meson.build
+++ b/meson.build
@@ -231,8 +231,7 @@
     )
 endif
 
-if (get_option('verify-signature').enabled() or \
-    get_option('verify-full-signature').enabled())
+if (get_option('verify-signature').enabled())
     image_updater_sources += files(
         'utils.cpp',
         'image_verify.cpp',