Remove OverlayAlgBase (ATLASSIM-3818)

This MR removes obsolete OverlayAlgBase algorithm and package.

unmarked as a Work In Progress

changed the description

This merge request affects 1 package:

• Event/EventOverlay/IDC_OverlayBase

Adding @jchapman ,@tkharlam ,@tadej ,@ahaas as watchers

added EDM Overlay master review-pending-level-1 labels

CI Result FAILURE

	Athena	AthSimulation
externals
cmake
make
required tests
optional tests

Full details available at NICOS MR-22063-2019-03-28-02-14
Athena: number of compilation errors 0, warnings 0
AthSimulation: number of compilation errors 0, warnings 0
For experts only: Jenkins output [CI-MERGE-REQUEST 36093]

CI failures unrelated.

added review-approved label and removed review-pending-level-1 label

merged

mentioned in commit d940970c

added sweep:ignore label