Revert "[TASK] Replace inject methods with @inject; allow @Flow\Inject"

This reverts commit ad7219c2

See https://review.typo3.org/#/c/21997/

More notes on this:
A regex to replace @inject with @Flow\Inject when porting 
Extbase extensions to Flow is very simple and fast.

Additionally @Flow\Inject makes only sense with using "use 
TYPO3\Flow\Annotations as Flow". But with a backported 
annotation parser I expect that we would have annotations 
in "TYPO3\CMS\Extbase\Annotations". Using them as alias 
"Flow" is a bad style as the alias should be "Extbase" then.

Change-Id: I2113b5320f2a6f5dd56cfa7b06469fa1628d2645
Reviewed-on: https://review.typo3.org/22004
Reviewed-by: Marc Bastian Heinrichs
Tested-by: Marc Bastian Heinrichs