Add RemoveDuplicatedEdges transform

[JakubPietrakIntel]

Removes duplicate edged to the given homogeneous or heterogeneous graph. It will change the original order of dataset by concatenating one of duplicated edges at the end of the dataset. It can be used to clean-up a known repeated self-connecting edges issue in ogbn-products. Reference to ogbn-products Leaderboard: here

Moved this to separate PR from #6699

[codecov]

Codecov Report

Merging #6709 (6f8b0ba) into master (844fc10) will increase coverage by 0.01%.
The diff coverage is 97.22%.

❗ Current head 6f8b0ba differs from pull request most recent head 7b1c3ea. Consider uploading reports for the commit 7b1c3ea to get more accurate results

@@            Coverage Diff             @@
##           master    #6709      +/-   ##
==========================================
+ Coverage   89.05%   89.06%   +0.01%     
==========================================
  Files         423      424       +1     
  Lines       22967    22998      +31     
==========================================
+ Hits        20453    20483      +30     
- Misses       2514     2515       +1     

Impacted Files	Coverage Δ
...ch_geometric/transforms/remove_duplicated_edges.py	94.73% <94.73%> (ø)
torch_geometric/nn/models/linkx.py	100.00% <100.00%> (ø)
torch_geometric/nn/models/mlp.py	95.18% <100.00%> (ø)
torch_geometric/transforms/__init__.py	100.00% <100.00%> (ø)

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