Revert ".travis.yml: grant access to mystamps database to travis user."

This reverts commit 0145ff4.

We don't need this workaround anymore as it was fixed on Travis CI recently:
https://docs.travis-ci.com/user/build-environment-updates/2017-09-06/#Fixed

Addressed to #612

Author: php-coder

.travis.yml

@@ -13,7 +13,6 @@ env:
 before_script:
   - if [ "$SPRING_PROFILES_ACTIVE" = 'travis' ]; then
       mysql -u root -e 'CREATE DATABASE mystamps CHARACTER SET utf8;';
-      mysql -u root -e 'GRANT ALL PRIVILEGES ON mystamps@* TO travis@%;';
       mkdir -p /tmp/uploads /tmp/preview;
       cp src/main/resources/test/test.png /tmp/uploads/1.png;
       if [ "$TRAVIS_BRANCH" = 'prod' -a "$TRAVIS_PULL_REQUEST" = 'false' ]; then