patch 8.1.0521: cannot build with +eval but without +quickfix

Problem:    Cannot build with +eval but without +quickfix.
Solution:   Remove #ifdef for e_stringreq. (John Marriott)
diff --git a/src/version.c b/src/version.c
index e3491a0..8aeda67 100644
--- a/src/version.c
+++ b/src/version.c
@@ -793,6 +793,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    521,
+/**/
     520,
 /**/
     519,