removed tipi test from CI suite because it's unstable

[Cyan4973]

I wonder if I should also remove the files in .tipi/ directory.

These files are essentially empty, so they don't seem to add much value.

On the other hand, I'm not sure if such an action would break something, like an external build system depending on this repository.

[t-mat]

Here are some logs about tipi.build for the record.

• Full acc loop #744 (comment)
• ci: fix tipi build error on github CI workflow #749
• remove tipi build temporary #759
• Feature: Support # comment lines in --check files #838

It's sad but it seems that tipi.build team keep introducing breaking changes to their environment without prior notices (from our point of view).

Since tipi.build is unstable and we don't how to test/stabilize it in our side, I think we should remove .tipi/ directory for now.
If someone is using it, they should fork xxHash and add their own "stable" .tipi/ settings. If we don't change .tipi/ directory anymore, they'll be able to git rebase easily.

Though I hope that we'll be able to re-introduce it when it'll be stabilized.