[RHEL/6, RHEL/7, shared] Fix 'Uninstall httpd & dovecot Package' rules & add (shared) remediations for them

This PR does the following (patch_1 for httpd package, patch_2 for dovecot package):
* fix 'Uninstall package_name Package' rule to use 'package_httpd/dovecot_removed' format (all three - rule ID, OVAL check & remediation to use same id / name prefix),
* updates profiles calling those (previously named rule) to use new name,
* move (previously RHEL/6 specific) OVAL check to be shared one (creating symlinks at appropriate places),
* create remediations for both packages, place them into shared & create symlinks at appropriate places.

Testing report:
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Proposal has been tested at both of RHEL-6 & RHEL-7 & works (at both) as expected.

Please review.

Thank you, Jan.

P.S.: There are more rules which will require similar change (e.g. vsftpd etc.) but given this type of change requires to change ~15 files per package, splitting them into multiple pull requests (for easier review).