Externals Update, master branch (2021.04.21.)

Updated all the projects to atlasexternals-2.0.105. The updates wrt. to atlasexternals-2.0.104 are the following (atlasexternals@2.0.104...2.0.105):

• Updated FindSuperchic.cmake to add the Superchic executables to the environment, and set up SUPERCHICPATH in the runtime environment as well (thanks to @wmccorma);
• Removed the PACKAGE_VERSION_UQ definition from the compilation commands (thanks to @fwinkl);
• Added the ATLAS_PACKAGE_NAME definition to all compilation commands executed in "ATLAS packages";
• Removed the global setting of the HAVE_64_BITS, __IDENTIFIER_64BIT__ and FVOIDP compiler definitions.

The removal of PACKAGE_VERSION_UQ is related to the discussion going on in ATEAM-731, and @fwinkl's changes in !42543 (merged).

I also wanted to get rid of the global setting of HAVE_64_BITS, __IDENTIFIER_64BIT__ and FVOIDP for a long time now, and Frank's changes were a good trigger to do that now. As it turns out, we've not been using HAVE_64_BITS anywhere in our code by now, and __IDENTIFIER_64BIT__ was used in exactly one place. I removed the logic from that one place, since we'll not be going back to 32-bit identifiers at any point by now.

FVOIDP has a couple of users, but in the greater scheme of things, it was still better to set that definition specifically in those 3 places than to turn it on globally for all Fortran compilation commands in this repository.

Because of the PACKAGE_VERSION_UQ removal I think a thorough test is warranted for this MR... (It should be safe to merge afterwards, full-build should not scare the release manager. I'm only turning it on to make sure that nothing would be left over from previous builds with that flag still set.)