Fix disco for MAM MIM-1412

[arcusfelis]

This PR addresses MIM-1412 "not working disco for mod_mam".

Proposed changes include:

• just use HostType.

[codecov]

Codecov Report

Merging #3155 (3e58495) into master (bc02e78) will decrease coverage by 0.02%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #3155      +/-   ##
==========================================
- Coverage   79.85%   79.83%   -0.03%     
==========================================
  Files         396      396              
  Lines       32343    32343              
==========================================
- Hits        25829    25820       -9     
- Misses       6514     6523       +9     

Impacted Files	Coverage Δ
src/mam/mod_mam.erl	88.88% <100.00%> (ø)
src/mam/mod_mam_muc.erl	73.63% <100.00%> (ø)
src/mam/mod_mam_utils.erl	89.89% <100.00%> (ø)
src/pubsub/node_hometree.erl	77.77% <0.00%> (-5.56%)	⬇️
src/ejabberd_s2s_out.erl	60.13% <0.00%> (-1.83%)	⬇️
src/ejabberd_c2s.erl	89.06% <0.00%> (-0.52%)	⬇️
src/mod_muc_room.erl	77.10% <0.00%> (+0.17%)	⬆️
src/ejabberd_sm.erl	84.59% <0.00%> (+0.32%)	⬆️
src/pubsub/mod_pubsub_db_mnesia.erl	92.82% <0.00%> (+0.42%)	⬆️
src/ejabberd.erl	55.00% <0.00%> (+10.00%)	⬆️

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[chrzaszcz]

Looks good!

[chrzaszcz]

Great!