[tests] Delete disabled test file (#2996)

This test has been disabled for years, it's extremely unimportant (tests
for enums with 2^16 variants), and is almost certainly unneeded anyway
since the same codepaths are tested by the `repr(u8)` case.

gherrit-pr-id: Gcfda5f0363b5a5e71c291bfc1a4ab75405ac6c13

Author: joshlf