remove support for running post lock command

This command was used for example to suspend-to-ram (man page example).

On Linux running this command inherits OOM killer immunity. This could be
abused by an other local user on the same machine (abusing resources).

To keep the use-case for suspend-to-ram an user could write a wrapper script
for it, outside the scope of slock.

Simplify argument handling, because the post-lock command parameter is removed.

Reported by: Acts1631 <acts1631kjv@proton.me>

Makefile

@@ -11,7 +11,7 @@ all: slock
 .c.o:
 	${CC} -c ${CFLAGS} $<
 
-${OBJ}: config.h config.mk arg.h util.h
+${OBJ}: config.h config.mk util.h
 
 config.h:
 	cp config.def.h $@
@@ -25,7 +25,7 @@ clean:
 dist: clean
 	mkdir -p slock-${VERSION}
 	cp -R LICENSE Makefile README slock.1 config.mk \
-		${SRC} config.def.h arg.h util.h slock-${VERSION}
+		${SRC} config.def.h util.h slock-${VERSION}
 	tar -cf slock-${VERSION}.tar slock-${VERSION}
 	gzip slock-${VERSION}.tar
 	rm -rf slock-${VERSION}