Remove repo-wide gitignore file

[redbrogdon]

Now that we have so many individual projects, some of which are traditional Android and iOS apps, we need to remove the repo's overall .gitignore and standardize the project-level ignore files.

[arteevraina]

Hello @redbrogdon I want to start my contribution to this repo. Can I take up this issue?

[redbrogdon]

In addition, the gitignores for each sample should be checked to make sure they match the ones currently created by flutter create.

[Bhavay-2001]

Hello @redbrogdon I would like to work on this issue , can u help me with any way possible please ??