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_global_arr_u8/case.ww

@@ -0,0 +1,9 @@
+//ww:run-exit 42
+// Migrated from 700_e2e row 121.
+package main;
+let buf: [4]u8;
+fn main() i32 = {
+  buf[0] = 7u8;
+  buf[1] = 35u8;
+  return (buf[0] + buf[1]): i32;
+};