patch 8.1.1990: cannot build with eval but without cscope

Problem:    Cannot build with eval but without cscope.
Solution:   Always include if_cscope.pro.
diff --git a/src/proto.h b/src/proto.h
index 0eafcc4..0c5a71f 100644
--- a/src/proto.h
+++ b/src/proto.h
@@ -68,9 +68,7 @@
 # include "charset.pro"
 # include "cmdexpand.pro"
 # include "cmdhist.pro"
-# ifdef FEAT_CSCOPE
-#  include "if_cscope.pro"
-# endif
+# include "if_cscope.pro"
 # include "debugger.pro"
 # include "dict.pro"
 # include "diff.pro"