add E_BINDING_CONTEXT_LAST as sentinal enum value

also remove suspicious-but-unused E_BINDING_CONTEXT_NUMBER define
in mousebindings

src/bin/e_bindings.h

@@ -11,7 +11,8 @@ typedef enum _E_Binding_Context
    E_BINDING_CONTEXT_MENU,
    E_BINDING_CONTEXT_WINLIST,
    E_BINDING_CONTEXT_POPUP,
-   E_BINDING_CONTEXT_ANY
+   E_BINDING_CONTEXT_ANY,
+   E_BINDING_CONTEXT_LAST,
 } E_Binding_Context;
 
 /* why do we do this? config stored bindings must be fixed. x's modifier masks

src/modules/conf_bindings/e_int_config_mousebindings.c

@@ -2,7 +2,6 @@
 
 #define TEXT_NO_PARAMS                     _("<None>")
 #define EXAMPLE_STRING                     "example : "
-#define E_BINDING_CONTEXT_NUMBER           10
 
 #define TEXT_PRESS_MOUSE_BINIDING_SEQUENCE _("Please hold any modifier you want<br>"            \
                                              "and press any button on your mouse,<br>or roll a" \