crypto/bn256: full switchover to cloudflare's code (#16301)

* crypto/bn256: full switchover to cloudflare's code

* crypto/bn256: only use cloudflare for optimized architectures

* crypto/bn256: upstream fallback for non-optimized code

* .travis, build: drop support for Go 1.8 (need type aliases)

* crypto/bn256/cloudflare: enable curve mul lattice optimization

.travis.yml

@@ -3,17 +3,6 @@ go_import_path: github.com/ethereum/go-ethereum
 sudo: false
 matrix:
   include:
-    - os: linux
-      dist: trusty
-      sudo: required
-      go: 1.8.x
-      script:
-        - sudo modprobe fuse
-        - sudo chmod 666 /dev/fuse
-        - sudo chown root:$USER /etc/fuse.conf
-        - go run build/ci.go install
-        - go run build/ci.go test -coverage
-
     - os: linux
       dist: trusty
       sudo: required