MDL-52472 travis: remove mongo/memcached testing

At the moment the extensions aren't available in php7 env:
https://github.com/travis-ci/travis-ci/issues/5256

And really its probably not worth the effort/buildtime to
enable them IMO so simpler to just disable.

.travis.yml

@@ -18,11 +18,6 @@ php:
     # - 5.5
     - 5.4
 
-services:
-    # Ensure that memcached and mongodb are running for testing of those MUC stores.
-    - memcached
-    - mongodb
-
 env:
     # Although we want to run these jobs and see failures as quickly as possible, we also want to get the slowest job to
     # start first so that the total run time is not too high.
@@ -71,10 +66,6 @@ install:
     # Typically it should be able to use the Composer cache if any other job has already completed before we started here.
     - travis_retry composer install --prefer-dist --no-interaction
 
-    - echo "extension = memcache.so" >> ~/.phpenv/versions/$(phpenv version-name)/etc/php.ini
-    - echo "extension = memcached.so" >> ~/.phpenv/versions/$(phpenv version-name)/etc/php.ini
-    - echo "extension = mongo.so" >> ~/.phpenv/versions/$(phpenv version-name)/etc/php.ini
-
 before_script:
     - >
       if [ "$INSTALL" = 'true' -o "$PHPUNIT" = 'true' ];
@@ -129,9 +120,6 @@ before_script:
           sed -i \
             -e "/require_once/i \\\$CFG->phpunit_dataroot = '\/home\/travis\/roots\/phpunit';" \
             -e "/require_once/i \\\$CFG->phpunit_prefix = 'p_';" \
-            -e "/require_once/i define('TEST_CACHESTORE_MEMCACHE_TESTSERVERS', '127.0.0.1:11211');" \
-            -e "/require_once/i define('TEST_CACHESTORE_MEMCACHED_TESTSERVERS', '127.0.0.1:11211');" \
-            -e "/require_once/i define('TEST_CACHESTORE_MONGODB_TESTSERVER', 'mongodb://localhost:27017');" \
             config.php ;
 
           # Initialise PHPUnit for Moodle.