Remove xsaves from Zen cpuspec

[vchuravy]

Fixes #50102

As far as I understand it xsaves is broken on zenver1 and zenver2, and the Linux kernel disables that.
Weirdly enough in #50102 we are running on AMD EPYC 7B13 which is zenver3 and the it reports not having xsaves.

I don't think we are using it (maybe we should look into xsavec for task-switching xD )
so it should be safe to remove it from the set of required extensions.

[giordano]

For the record, I noticed archspec-json doesn't list xsaves anywhere. I asked @alalazo on Spack slack about why this feature is completely ignored and the answer was

Iirc this dates back to the initial implementation of archspec, and we noticed (2019) that XSAVES was not reliably exposed on all operating systems. Given that:

1. If not exposed, it prevented the detection of architecture that could use AVX512
2. It wasn't the only instruction that allowed to distinguish between two architectures

we decided to leave it out on detection