Revert "net/http: FileServer method check + minimal OPTIONS implementation"

Revert "net/http: FileServer method check + minimal OPTIONS implementation"

This reverts https://go.dev/cl/413554

Reason for revert: Backwards-incompatible change in behavior.

For #53501
For #59375

Change-Id: Ic3f63b378f9c819599b32e5e6e410f6163849317
Reviewed-on: https://go-review.googlesource.com/c/go/+/482635
Reviewed-by: Tatiana Bradley <tatianabradley@google.com>
Run-TryBot: Damien Neil <dneil@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>