Upgrade grep(1). 2/2

Adapt master branch to vendor update:

- update README.DELETED and README.DRAGONFLY
- re-generate header files
- adapt build
- sync manpage grep.1 with vendor

Reviewed by: Sasc

Upgrade grep(1). 2/2

Adapt master branch to vendor update:

- update README.DELETED and README.DRAGONFLY
- re-generate header files
- adapt build
- sync manpage grep.1 with vendor

Reviewed by: Sascha Wildner

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