Remote ApplicationInsights.config from VisualStudio.gitignore

Commit a25589c9 introduced an ignore line for ApplicationInsights.config. This change breaks builds on certain systems, namely VSTS.

The current ASP.NET 4 template adds ApplicationInsights.config to the project's .csproj file. When VSTS attempts to build the project, it will fail if it cannot find ApplicationInsights.config.

ApplicationInsights.config is a required application file and should not be ignored.