Fix duplicate loading of eras in mp

This fixes warnings about the era macros being redefined without being #undef-ed when
loading MP.

data/_main.cfg

@@ -30,11 +30,11 @@
 {test/multiplayer/}
 #endif
 
-#else
-# using different default eras in sp and mp forcesus to a config reload which we dont want.
-{multiplayer/eras.cfg}
 #endif
 
+# Using different default eras in SP and MP forces a config reload which we don't want.
+{eras.cfg}
+
 {campaigns/}
 
 [ais]

data/eras.cfg

@@ -16,7 +16,7 @@
     [event]
         name=prestart
         [lua]
-            code = << wesnoth.require("multiplayer/eras.lua").quick_4mp_leaders(...) >>
+            code = << wesnoth.require("eras.lua").quick_4mp_leaders(...) >>
             [args]
                 {TRAIT_QUICK}
             [/args]
@@ -28,7 +28,7 @@
     [event]
         name=time over
         [lua]
-            code = << wesnoth.require("multiplayer/eras.lua").turns_over_advantage() >>
+            code = << wesnoth.require("eras.lua").turns_over_advantage() >>
         [/lua]
     [/event]
 #enddef

data/multiplayer/_main.cfg

@@ -14,8 +14,6 @@
 
 {multiplayer/scenarios/}
 
-{multiplayer/eras.cfg}
-
 [lobby_music]
     {DEFAULT_MUSIC_PLAYLIST}
     [music]