Revert "Build PHP 7.4.0"

This reverts commit 0e41179.

php-build has recently added 7.4 support, so we'll use that instead.

php-build/php-build#599

.travis.yml

@@ -195,7 +195,7 @@ before_install:
   - php -f test.php || true
 
 install:
-- if [[ ! -d $HOME/.php-build ]]; then git clone https://github.com/DamianSzymanski/php-build.git $HOME/.php-build; fi
+- if [[ ! -d $HOME/.php-build ]]; then git clone https://github.com/php-build/php-build.git $HOME/.php-build; fi
 - rm -rf $HOME/.phpenv
 - git clone 'https://github.com/phpenv/phpenv.git' $HOME/.phpenv
 - eval "$($HOME/.phpenv/bin/phpenv init -)"