Remove disabled command cede

It misuses snxtsct() and snxtitem() to find out whether the first
argument looks like sectors or like ships, which doesn't work with a
bad conditional argument.

Not worth fixing now; it's been disabled since 4.0.1, and broken at
least since commit 2fc1e74a (v4.3.0) broke its sector/ship
disambiguation via third argument.

include/prototypes.h

@@ -94,7 +94,6 @@ int buil(void);
 int buy(void);
 int capi(void);
 int carg(void);
-int cede(void);
 int cens(void);
 int chan(void);
 int coas(void);