ci: simplify Travis config

Travis CI has improved a lot since this file was created and overall the
new defaults are good enough to achieve the level of testing that the
original file contained.

.travis.yml

@@ -10,31 +10,3 @@ cache: cargo
 matrix:
   allow_failures:
   - rust: nightly
-before_script:
-- |
-  pip install 'travis-cargo<0.2' --user &&
-  export PATH=$HOME/.local/bin:$PATH
-script:
-- |
-  travis-cargo build &&
-  travis-cargo test &&
-  travis-cargo bench &&
-  travis-cargo --only stable doc
-addons:
-  apt:
-    sources:
-    - kalakris-cmake
-    packages:
-    - cmake
-    - libcurl4-openssl-dev
-    - libelf-dev
-    - libdw-dev
-after_success:
-- travis-cargo --only stable doc-upload
-notifications:
-  email:
-    on_success: never
-env:
-  global:
-    - TRAVIS_CARGO_NIGHTLY_FEATURE=""
-    - secure: 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