Remove elixxir libraries

.gitlab-ci.yml

Makefile

csprng/source.go

csprng/source_test.go

csprng/systemRNG.go

csprng/systemRNG_test.go

go.mod

go.sum

large/int.go

large/int_test.go

nonce/nonce.go

signature/genericSigning.go

signature/rsa/rsa.go

testkeys/cmix.rip.crt

testkeys/cmix.rip.key

testkeys/keypath.go

tls/credentials.go

tls/credentials_test.go