Remove unused define

src/doomdef.h

@@ -562,10 +562,6 @@ extern const char *compdate, *comptime, *comprevision, *compbranch;
 // None of these that are disabled in the normal build are guaranteed to work perfectly
 // Compile them at your own risk!
 
-/// Backwards compatibility with SRB2CB's slope linedef types.
-///	\note	A simple shim that prints a warning.
-#define ESLOPE_TYPESHIM
-
 ///	Allows the use of devmode in multiplayer. AKA "fishcake"
 //#define NETGAME_DEVMODE