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_bytes_index/case.ww

@@ -0,0 +1,18 @@
+//ww:run-exit 7
+// Migrated from 700_e2e row 101.
+package main;
+import bytes;
+fn main() i32 = {
+  let buf: [12]u8;
+  buf[0] = 104u8; buf[1] = 101u8; buf[2] = 108u8; buf[3] = 108u8;
+  buf[4] = 111u8; buf[5] = 44u8;  buf[6] = 32u8;  buf[7] = 119u8;
+  buf[8] = 111u8; buf[9] = 114u8; buf[10] = 108u8; buf[11] = 100u8;
+  let needle: [3]u8;
+  needle[0] = 119u8; needle[1] = 111u8; needle[2] = 114u8;
+  let r: (i32 | void) = bytes.index(buf[0:12], needle[0:3]);
+  match (r) {
+    case let i: i32 => return i;
+    case void => return -1;
+  };
+  return 0;
+};