test: remove package-wide import assumptions

test/wcc/data/r75_alloc_str_readback/case.ww

@@ -1,5 +1,4 @@
 //ww:run-exit 209
 package main;
-import rt;
 type holder = struct { s: str };
 fn main() i32 = { let p: *holder = alloc(holder { s = "hi" })!; let sum: i32 = 0; let i: i32 = 0; for (i < p.s.len) { sum += p.s[i]: i32; i += 1; }; return sum; };