simplified memcache installation on travis

tests/unit/data/travis/memcache-setup.sh

 #!/bin/sh
 
-install_memcache() {
-#    if [ "$(expr "$TRAVIS_PHP_VERSION" ">=" "5.5")" -eq 1 ]; then
-#        MEMCACHE_VERSION="2.2.7"
-#        wget "http://pecl.php.net/get/memcache-$MEMCACHE_VERSION.tgz" &&
-#        tar -zxf "memcache-$MEMCACHE_VERSION.tgz" &&
-#        sh -c "cd memcache-$MEMCACHE_VERSION && phpize && ./configure --enable-memcache && make && sudo make install"
-#    fi
-
-    echo "extension=memcache.so" >> ~/.phpenv/versions/$(phpenv version-name)/etc/php.ini
-
-    return $?
-}
-
-install_memcache > ~/memcache.log || ( echo "=== MEMCACHE BUILD FAILED ==="; cat ~/memcache.log )
-
+echo "extension=memcache.so" >> ~/.phpenv/versions/$(phpenv version-name)/etc/php.ini
 echo "extension=memcached.so" >> ~/.phpenv/versions/$(phpenv version-name)/etc/php.ini