patch 8.2.4010: error messages are spread out

Problem:    Error messages are spread out.
Solution:   Move more error messages to errors.h.
diff --git a/src/float.c b/src/float.c
index ee0ceda..ef9b830 100644
--- a/src/float.c
+++ b/src/float.c
@@ -99,7 +99,7 @@
 	*f = (float_T)argvars[0].vval.v_number;
 	return OK;
     }
-    emsg(_("E808: Number or Float required"));
+    emsg(_(e_number_or_float_required));
     return FAIL;
 }