TreeDefinition.Remove fails to remove unwrapped trees.

[tyrielv]

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Reproduction steps

var dir = Path.GetTempPath() + Path.GetRandomFileName();
Repository.Init(dir);
Repository r = new Repository(dir);
Blob empty = r.ObjectDatabase.CreateBlob(new MemoryStream());
var td = new TreeDefinition();
td.Add("a/b/c", empty, Mode.NonExecutableFile);
td.Remove("a");
bool presentInTreeDefinition = td["a"] != null;
Tree t = r.ObjectDatabase.CreateTree(td);
bool presentInTree = t["a"] != null;

Expected behavior

Both presentInTreeDefinition and presentInTree should be false.

Actual behavior

presentInTreeDefinition is false, but presentInTree is true.

Version of LibGit2Sharp (release number or SHA1)

0.26.2

Operating system(s) tested; .NET runtime tested

Windows 10, .NET Core 3.1

[tyrielv]

libgit2sharp/LibGit2Sharp/TreeDefinition.cs

Line 96 in df3b22a

entries.Remove(segments.Item1);

The tree entry is removed here, but the private field unwrapped tree is not removed unless it already has no subentries.
When the tree is built from the definition, the still-present unwrapped tree reintroduces what should have been removed.