Remove Travis CI configuration (#484)

The migration to GitHub Actions occurred quite awhile ago and Travis CI
is no longer used

Author: tarcieri

.travis.yml

@@ -21,7 +21,6 @@ description = "A pure-Rust implementation of group operations on ristretto255 an
 exclude = [
     "**/.gitignore",
     ".gitignore",
-    ".travis.yml",
 ]
 
 [package.metadata.docs.rs]
@@ -32,9 +31,6 @@ rustdoc-args = [
 rustc-args = ["--cfg", "curve25519_dalek_backend=\"simd\""]
 features = ["serde", "rand_core", "digest"]
 
-[badges]
-travis-ci = { repository = "dalek-cryptography/curve25519-dalek", branch = "master"}
-
 [dev-dependencies]
 sha2 = { version = "0.10", default-features = false }
 bincode = "1"