Remove QQBar export

[lgoettgens]

Resolves parts of #1379.

For my convenience, this already includes the changes of #2444, and will be rebased, once that has been merged.

This PR is a draft until the scope has been discussed in #1379.

[codecov]

Codecov Report

Merging #2445 (6285015) into master (4f06d82) will decrease coverage by 0.03%.
The diff coverage is n/a.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2445      +/-   ##
==========================================
- Coverage   73.08%   73.05%   -0.03%     
==========================================
  Files         397      397              
  Lines       53449    53449              
==========================================
- Hits        39061    39049      -12     
- Misses      14388    14400      +12     

see 5 files with indirect coverage changes

[fingolfin]

This needs a rebase.

[fingolfin]

Removing QQBar from the export list was already agreed upon in #1379, wasn't it?

In any case, can't hurt to have @fieker or @thofma have another look at this, too

[lgoettgens]

This now only removes QQBar export. For the other things, the discussion will be held in #1379 and I will create a new PR afterwards.