removed superfluous examples

examples/NCH-18/linear/C4B_t15.imp

@@ -3,7 +3,7 @@
 def f():
     var x, y, t, r
     assume y >= 0
-    while x > y:
+    while [y >= 0] x > y:
     	x = x - y
     	x = x - 1
     	t = y

examples/NCH-18/linear/C4B_t15_2.imp

-# t15 in C4B figure 8
-
-def f():
-    var x, y, t, r
-    assume y >= 0
-    while [y >= 0] x > y:
-    	x = x - y
-    	x = x - 1
-    	t = y
-    	while t > 0:
-        	r = unif(0,1)
-        	t = t - r
-        	tick 1
-
-    	tick 1

examples/NCH-18/linear/C4B_t30.imp

@@ -2,7 +2,7 @@
 
 def f():
     var x, y, t, r
-    while x > 0:
+    while [y >= -1] x > 0:
         r = unif(1, 3)
         x = x - r
         t = x

examples/NCH-18/linear/C4B_t30_2.imp

-# t30 in C4B figure 8
-
-def f():
-    var x, y, t, r
-    while [y >= -1] x > 0:
-        r = unif(1, 3)
-        x = x - r
-        t = x
-        x = y
-        y = t
-        tick 1