Externals Update, 21.2 branch (2020.04.14.)

Switched all projects to atlasexternals-1.0.62.

The full list of changes wrt. atlasexternals-1.0.61 is (atlasexternals@1.0.61...1.0.62):

• Bumped the version of MCUtils to 1.3.4 in AnalysisBaseExternals and AthAnalysisExternals;
• Removed the unnecessary -c argument from the CINT dictionary generation calls;
• Enabled the build of Minuit2 for/with ROOT 6.18/04.

At the same time made sure that AthAnalysis and AthDerivation would both correctly pick up MCUtils-1.3.4, by adjusting/removing the appropriate files. (This part is a replacement for !31727 (closed).)