meson: remove dead variable

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
diff --git a/ui/meson.build b/ui/meson.build
index 7faa42e..a73beb0 100644
--- a/ui/meson.build
+++ b/ui/meson.build
@@ -105,8 +105,6 @@
   ui_modules += {'spice-app': spice_ss}
 endif
 
-keymap_gen = find_program('keycodemapdb/tools/keymap-gen')
-
 keymaps = [
   ['atset1', 'qcode'],
   ['linux', 'qcode'],