test: migrate 700_e2e rows to corpus fixtures; retire the carrier

136 rows migrated, 0 already owned, 3 wwstage-failing rows held out.

test/wcc/data/r700_rt_malloc_free/case.ww

@@ -0,0 +1,14 @@
+//ww:run-exit 0
+// Migrated from 700_e2e row 20.
+package main;
+import os;
+import rt;
+fn main() i32 = {
+  let p: *void = rt.malloc(4096u64);
+  if (p == nil) { return 1; };
+  let bp: *u8 = p: *u8;
+  bp[0] = 65u8;
+  os.write(1, bp, 1u64);
+  os.free(p, 4096u64);
+  return 0;
+};