Remove the x86 build/test from the CI.

[qinkunbao]

Remove the x86 build/test from the CI from the CI for the following reasons.

1. Our CVMs only support x86-64.
2. Some dependency libraries (go-tdx-guest, go-sev-guest) are only tested with x86-64.
3. go-tpm-tools releases only have x86-64.

[JoshuaKrstic]

/gcbrun

[jkl73]

CVM is not the only platform this tool/lib can run.
Majority features on gotpm cli and libs are not depending on go-tdx-guest/go-sev-guest
Users may still want to build the binary on a 32 bit system.

[jkl73]

So I think we probably should keep x86 build/test in CI, unless it's so broken and beyond fix.