Remove FlashMessenger view helper

[alextech]

Remove FlashMessenger view helper as requested by zendframework/zend-mvc-plugin-flashmessenger#3

Complementary port to MVC Plugin PR is at zendframework/zend-mvc-plugin-flashmessenger#10

[samsonasik]

needs rebase

[weierophinney]

This repository has been closed and moved to laminas/laminas-view; a new issue has been opened at laminas/laminas-view#16.

[weierophinney]

This repository has been moved to laminas/laminas-view. If you feel that this patch is still relevant, please re-open against that repository, and reference this issue. To re-open, we suggest the following workflow:

• Squash all commits in your branch (git rebase -i origin/{branch})
• Make a note of all changed files (`git diff --name-only origin/{branch}...HEAD
• Run the laminas/laminas-migration tool on the code.
• Clone laminas/laminas-view to another directory.
• Copy the files from the second bullet point to the clone of laminas/laminas-view.
• In your clone of laminas/laminas-view, commit the files, push to your fork, and open the new PR.
  We will be providing tooling via laminas/laminas-migration soon to help automate the process.