fix bug: when deleting a hybrid edge leads to simplification of parallel edges at hybrid with 2 children

[cecileane]

to fix this error:

julia> n = readTopology("(a:0.003,((#H3:0::0.003,(b:0.2,c:0.2)#H1:0.3::1):0.3,(#H1:0::0)#H3:0::0.997):0);");

julia> majorTree(n)
ERROR: node 5 has no minor parent

which occurs because after this:

PhyloNetworks.deletehybridedge!(n, n.edge[2])

node number 4, H1, is still marked as hybrid but only 1 parent (tree) edge. Originally, H1 had 2 parents and 2 children.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (9e93501) 86.83% compared to head (1b781d9) 86.79%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #207      +/-   ##
==========================================
- Coverage   86.83%   86.79%   -0.05%     
==========================================
  Files          31       31              
  Lines       12623    12635      +12     
==========================================
+ Hits        10961    10966       +5     
- Misses       1662     1669       +7     

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