remove user and platform specific files from `.gitignore`

Users should instead configure a local excludes file by placing
the following into the per-user `~/.gitconfig` for example.

````
[core]
        excludesFile = ~/.gitignore
````

Now it's easy to generaet a suitable `~/.gitignore` file using
https://gitignore.io for instance.

1 files changed, 0 insertions, 7 deletions

diff --git a/.gitignore b/.gitignore
index bc4db33..627fbdd 100644
--- a/.gitignore
+++ b/.gitignore
@@ -10,10 +10,3 @@
 
 # These are backup files generated by rustfmt
 **/*.rs.bk
-
-/.idea/
-/.vscode/
-
-/callgrind.profile
-
-.DS_Store