crypto/elliptic: delete outdated fuzz test

It had not been doing anything since CL 233939, because the Params
method was getting upgraded to the assembly one. We could make it use
genericParamsForCurve, but really we need lower-level, targeted Go 1.18
fuzz targets in nistec now.

Change-Id: I5b198a309aa90ecef9c04aaa6c107d5c0a41a44b
Reviewed-on: https://go-review.googlesource.com/c/go/+/396254
Run-TryBot: Filippo Valsorda <[email protected]>
Trust: Filippo Valsorda <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>
Reviewed-by: Roland Shoemaker <[email protected]>

Author: FiloSottile