Remove `virtual` qualifiers on member functions of a `final` class

RegistryEntry is marked final, but qualifies some methods as virtual. This MR removes these virtual qualifiers.

• [2017-11-22 10:57] Validation started with lhcb-gaudi-merge#321
• [2017-11-23 00:02] Validation started with lhcb-future#610
• [2017-11-23 00:03] Validation started with lhcb-gaudi-head#1667
• [2017-11-23 00:03] Validation started with lhcb-future-clang#384
• [2017-11-24 00:03] Validation started with lhcb-future-clang#385
• [2017-11-24 00:03] Validation started with lhcb-gaudi-head#1668
• [2017-11-24 00:05] Validation started with lhcb-future#611
• [2017-11-25 00:03] Validation started with lhcb-gaudi-head#1669
• [2017-11-25 00:03] Validation started with lhcb-future#612
• [2017-11-25 00:03] Validation started with lhcb-future-clang#386
• [2017-11-26 00:03] Validation started with lhcb-future#613
• [2017-11-26 00:03] Validation started with lhcb-future-clang#387
• [2017-11-26 00:03] Validation started with lhcb-gaudi-head#1670
• [2017-11-27 00:04] Validation started with lhcb-gaudi-head#1671
• [2017-11-27 00:04] Validation started with lhcb-future#614
• [2017-11-27 00:04] Validation started with lhcb-future-clang#388
• [2017-11-27 12:43] Validation started with lhcb-gaudi-head#1672

approved this merge request

assigned to @hegner

changed milestone to %v30r1

mentioned in commit 4d6eba2d

merged

added code cleanup label