travis: Remove custom cmake

Travis provides cmake 3.9.2 ([1])

[1]:
https://docs.travis-ci.com/user/build-environment-updates/2017-12-12/

.travis.yml

@@ -8,7 +8,6 @@ env:
     - LLVM_URL="http://llvm.org/releases/${LLVM_VERSION}/llvm-${LLVM_VERSION}.src.tar.xz"
     - LIBCXX_URL="http://llvm.org/releases/${LLVM_VERSION}/libcxx-${LLVM_VERSION}.src.tar.xz"
     - LIBCXXABI_URL="http://llvm.org/releases/${LLVM_VERSION}/libcxxabi-${LLVM_VERSION}.src.tar.xz"
-    - CMAKE_URL="https://cmake.org/files/v3.6/cmake-3.6.2-Linux-x86_64.tar.gz"
     - JOBS=4
     - POLYBAR_BUILD_TYPE="compile"
 
@@ -41,11 +40,8 @@ addons:
     sources:
       - ubuntu-toolchain-r-test
       - llvm-toolchain-precise-3.8
-      - sourceline: "ppa:george-edison55/george-edison"
     packages:
       - clang-3.8
-      - cmake
-      - cmake-data
       - g++-5
       - gcc-5
       - i3-wm
@@ -68,7 +64,6 @@ addons:
 
 cache:
   directories:
-    - ${TRAVIS_BUILD_DIR}/deps/cmake
     - ${TRAVIS_BUILD_DIR}/deps/llvm-3.8.1/install
     - ${TRAVIS_BUILD_DIR}/deps/xcb-util-xrm
 
@@ -77,7 +72,6 @@ install:
   - mkdir -p "${DEPS_DIR}" && cd "${DEPS_DIR}"
   - source ${TRAVIS_BUILD_DIR}/common/travis/environment.sh
   - source ${TRAVIS_BUILD_DIR}/common/travis/install_xcb_xrm.sh
-  - source ${TRAVIS_BUILD_DIR}/common/travis/install_cmake.sh
   - source ${TRAVIS_BUILD_DIR}/common/travis/install_libcpp.sh
 
 before_script:

common/travis/install_cmake.sh

@@ -1,7 +0,0 @@
-#!/bin/bash
-if [ -z "$(ls -A "${DEPS_DIR}/cmake/bin" 2>/dev/null)" ]; then
-  mkdir -p "cmake"
-  travis_retry wget --no-check-certificate -O - "${CMAKE_URL}" | tar --strip-components=1 -xz -C cmake
-fi
-
-export PATH="${DEPS_DIR}/cmake/bin:${PATH}"