Remove deprecated build hacks. Includes move to CCE18 (Frontier)

[henryleberre]

• Removed CCE 16 workgroup hacks.
• Removed AppleClang workarounds on macOS, including building MPI from scratch.
• Only build FFTW and SILO packages if they are not installed/compatible (HDF5 not currently possible).
• Removed Docker (nobody uses it, and maintaining it is cumbersome).
• Switched to using the proper Silo patch for an error on GNU 13 and above. See my comment here: Silo does not compile with gcc 14 llnl/Silo#375 (comment).
• Removed installation instructions for Arch Linux. They installed their operating system, I'm sure they can install gcc.

Note from @sbryngelson: After this PR, use of <CCE18.0.0 will not be possible. Revert to previous release for use of CCE16.0.1 on Frontier/Tioga/El Capitan.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 54.69%. Comparing base (63c79cb) to head (d540220).
Report is 2 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #620   +/-   ##
=======================================
  Coverage   54.69%   54.69%           
=======================================
  Files          59       59           
  Lines       13662    13662           
  Branches     1698     1698           
=======================================
  Hits         7473     7473           
  Misses       5740     5740           
  Partials      449      449           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[sbryngelson]

Will merge once Phoenix is back up.