remove remaining is_not_empty functions/methods

src/test/run-pass/non-boolean-pure-fns.rs

@@ -23,7 +23,7 @@ pure fn pure_length<T: Copy>(ls: @List<T>) -> uint { pure_length_go(ls, 0u) }
 pure fn nonempty_list<T: Copy>(ls: @List<T>) -> bool { pure_length(ls) > 0u }
 
 fn safe_head<T: Copy>(ls: @List<T>) -> T {
-    assert is_not_empty(ls);
+    assert !is_empty(ls);
     return head(ls);
 }
 

src/test/run-pass/zip-same-length.rs

@@ -10,7 +10,7 @@
 
 // In this case, the code should compile and should
 // succeed at runtime
-use vec::{head, is_not_empty, last, same_length, zip};
+use vec::{head, last, same_length, zip};
 
 fn enum_chars(start: u8, end: u8) -> ~[char] {
     assert start < end;