Probuilder disappears from the package manager list as it does not compile when the package is removed once its sample project is imported and deleted. It is not available even after resetting the packages to default. Refer the attached video

Steps to reproduce:
1) Create a new project
2) Window > Package Manager
3) Install Probuilder package
4) Import Runtime sample
5) Delete runtime sample from project
6) Remove Probuilder package

Actual result: Probuilder disappears from the "All packages" list in package manager.
Expected result: Probuilder is present in "All packages" list in package manager.

Occurring in: 2019.3.0a11, 2019.3.0a10
Not reproducible in: 2019.3.0a9

Environment: Occurs on Windows. On Mac, there's an error while removing probuilder package and the user is unable to remove the package.

Stack trace:
Microsoft (R) Visual C# Compiler version 2.9.1.65535 (9d34608e)
Copyright (C) Microsoft Corporation. All rights reserved.

error CS2001: Source file 'F:\Delete\2019.3.0a11 new\Assets\Samples\ProBuilder\4.1.0\Runtime Examples\Convert Mesh to Editable\MakePrimitiveEditable.cs' could not be found.
error CS2001: Source file 'F:\Delete\2019.3.0a11 new\Assets\Samples\ProBuilder\4.1.0\Runtime Examples\Icosphere FFT\Scripts\IcoBumpin.cs' could not be found.
error CS2001: Source file 'F:\Delete\2019.3.0a11 new\Assets\Samples\ProBuilder\4.1.0\Runtime Examples\Icosphere FFT\Scripts\CameraControls.cs' could not be found.
error CS2001: Source file 'F:\Delete\2019.3.0a11 new\Assets\Samples\ProBuilder\4.1.0\Runtime Examples\Runtime Editing\Scripts\CameraMotion.cs' could not be found.
error CS2001: Source file 'F:\Delete\2019.3.0a11 new\Assets\Samples\ProBuilder\4.1.0\Runtime Examples\Misc\HueCube.cs' could not be found.
error CS2001: Source file 'F:\Delete\2019.3.0a11 new\Assets\Samples\ProBuilder\4.1.0\Runtime Examples\Runtime Editing\Scripts\MeshEditor.cs' could not be found.
error CS2001: Source file 'F:\Delete\2019.3.0a11 new\Assets\Samples\ProBuilder\4.1.0\Runtime Examples\Runtime Editing\Scripts\Handles.cs' could not be found.
error CS2001: Source file 'F:\Delete\2019.3.0a11 new\Assets\Samples\ProBuilder\4.1.0\Runtime Examples\Runtime Editing\Scripts\SimpleGrid.cs' could not be found.
error CS2001: Source file 'F:\Delete\2019.3.0a11 new\Assets\Samples\ProBuilder\4.1.0\Runtime Examples\Misc\CreatePolyShape.cs' could not be found.
error CS2001: Source file 'F:\Delete\2019.3.0a11 new\Assets\Samples\ProBuilder\4.1.0\Runtime Examples\Vertex Colors\HighlightNearestFace.cs' could not be found.
error CS2001: Source file 'F:\Delete\2019.3.0a11 new\Assets\Samples\ProBuilder\4.1.0\Runtime Examples\Runtime Editing\Scripts\Selection.cs' could not be found.
error CS2001: Source file 'F:\Delete\2019.3.0a11 new\Assets\Samples\ProBuilder\4.1.0\Runtime Examples\Procedural Mesh\ExtrudeRandomEdges.cs' could not be found.
error CS2001: Source file 'F:\Delete\2019.3.0a11 new\Assets\Samples\ProBuilder\4.1.0\Runtime Examples\Runtime Editing\Scripts\Utility.cs' could not be found.