Remove unnecessary nuget package in vs-extension

[RodgeFu]

Some transitive nuget package are added explicitly into vs-extension to avoid vulnerabilities and warnings. We need to remove them after the packages using them releases new versions with these vulnerabilities and warnings handled.

detail:

• The 'MessagePack' is not used directly but referenced by nuget package 'Microsoft.VisualStudio.SDK', 'Microsoft.VisualStudio.Workspace' and 'Microsoft.VisualStudio.VSIntegration'. Have to add it explicitly because the version used by 'Microsoft.VisualStudio...' report vulnerabilities now
• The 'Microsoft.VisualStudio.Composition' is not used directly but referenced by nuget package 'Microsoft.VisualStudio.Workspace'. Have to add it explicitly because otherwise 'Microsoft.VisualStudio.Workspace" will report warning NU1603 because its desired version not found and higher version will be used
• The 'Microsoft.VisualStudio.Shell.15.0' is not used directly but referenced by nuget package 'Microsoft.VisualStudio.Workspace.VSIntegration'. Have to add it explicitly because otherwise 'Microsoft.VisualStudio.Workspace.VSIntegration" will report warning NU1603 because its desired version not found and higher version will be used