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_f64_area/case.ww

@@ -0,0 +1,5 @@
+//ww:run-exit 78
+// Migrated from 700_e2e row 7.
+package main;
+fn area(r: f64) f64 = { return 3.14 * r * r; };
+fn main() i32 = { let a: f64 = area(5.0); return a: i32; };