cmake: use EPIC_ECCE_LEGACY_COMPAT=OFF

[veprbl]

Ideally, there would have been a warning message for users living with EPIC_ECCE_LEGACY_COMPAT=ON. But since many are only now learning things through the tutorials it makes sense to drop ECCE ASAP and reduce the confusion.

Briefly, what does this PR introduce?

A small follow up to yesterday's tutorial session. This removes unnecessary symlinks for users that are now just learning things.

What kind of change does this PR introduce?

• Bug fix (issue #__)
• New feature (issue #__)
• Documentation update
• Other: __

Please check if this PR fulfills the following:

• Tests for the changes have been added
• Documentation has been added / updated
• Changes have been communicated to collaborators

Does this PR introduce breaking changes? What changes might users need to make to their code?

No.

Does this PR change default behavior?

Supposedly, yes.

[veprbl]

-------- WWWW ------- G4Exception-START -------- WWWW -------
*** G4Exception : GeomVol1002
      issued by : G4PVPlacement::CheckOverlaps()
Overlap with volume already placed !
          Overlap is detected for volume AV_586!InnerMPGDBarrel_Mod1_88#88!component1_1#1:90 (G4Box)
          apparently fully encapsulating volume AV_585!InnerMPGDBarrel_Mod1_87#87!component0_0#0:88 (G4Box) at the same level!
NOTE: Reached maximum fixed number -1- of overlaps reports for this volume !
*** This is just a warning message. ***
-------- WWWW -------- G4Exception-END --------- WWWW -------

Is this supposed to happen, or issue-worthy?

[wdconinc]

It's issue worthy, @mposik1983 . It was probably always there but has shown up irregularly since we went to geant4 11.