Remove needlessly complex key generation scheme

[xacrimon]

While looking into TEL-Q122-11 which recommends we encrypt keys in the keygen function, I discovered that the suggested encryption is insecure and the entire encryption scheme is deprecated as of Go 1.16. To prevent confusion, I decided to remove the pass parameter from the keygen functions since it isn't actually used anywhere. Upon doing that, I discovered a host of wierd things like remote keygen HTTP APIs and overused indirection that I can't see they serve any purpose. This PR cleans all that up and uses native.GenerateKeyPair() for all keypair generation in Teleport.

[zmb3]

Should we leverage

teleport/lib/auth/native/native.go

Line 128 in bb121d7

func (k *Keygen) precomputeKeys() {

more?

This basically always has a keypair ready for you, waiting for you to pull it from a channel. I recall cloud using it in a few places to decrease latency.

[xacrimon]

@zmb3 Rewritten the system quite a bit, it now keeps a global key cache which should decrease latency application wide, including tests.