minor #12277 Removing the tests for PHP 7.0 (Kynno)

This PR was merged into the 4.3 branch.

Discussion
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Removing the tests for PHP 7.0

As Symfony 4 requires minimum PHP 7.1, some builds testing PHP 7.0 will automatically fail.

Also, I want to mention that the builds line 199 and 201 are not running because of the following error:
```
PHP Warning:  fopen(https://github.com/sebastianbergmann/phpunit/archive/6.3.zip): failed to open stream: HTTP request failed! HTTP/1.0 404 Not Found
```
If I remember well, some months ago PHPUnit removed all old available version and I guess that's what's causing the error

Commits
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d85f6c4 Removing the tests for PHP 7.0

Author: javiereguiluz

bundles/best_practices.rst

@@ -198,11 +198,10 @@ of Symfony and the latest beta release:
               # Minimum supported dependencies with the latest and oldest PHP version
             - php: 7.2
               env: COMPOSER_FLAGS="--prefer-stable --prefer-lowest" SYMFONY_DEPRECATIONS_HELPER="max[self]=0"
-            - php: 7.0
+            - php: 7.1
               env: COMPOSER_FLAGS="--prefer-stable --prefer-lowest" SYMFONY_DEPRECATIONS_HELPER="max[self]=0"
 
               # Test the latest stable release
-            - php: 7.0
             - php: 7.1
             - php: 7.2
               env: COVERAGE=true PHPUNIT_FLAGS="-v --coverage-text"