Remove the word "either" (#1938)

This is likely there because there are two different paths
depending on if the module was loaded as a network or a user
module. But only one of them is printed here so either does
not make any sense.

modules/cert.cpp

@@ -41,7 +41,7 @@ class CCertMod : public CModule {
                 "You do not have a certificate. Please use the web interface "
                 "to add a certificate"));
             if (GetUser()->IsAdmin()) {
-                PutModule(t_f("Alternatively you can either place one at {1}")(
+                PutModule(t_f("Alternatively you can place one at {1}")(
                     PemFile()));
             }
         }