remove section about alias imports (#22585)

this is not relevant anymore since we removed
all aliased imports.

contribute/style-guides/backend.md

@@ -39,7 +39,3 @@ Tests must use the standard library, `testing`. For assertions, prefer using [te
 The majority of our tests uses [GoConvey](http://goconvey.co/) but that's something we want to avoid going forward.
 
 In the `sqlstore` package we do database operations in tests and while some might say that's not suited for unit tests. We think they are fast enough and provide a lot of value.
-
-## General guidelines
-
-- Avoid using import aliases, e.g. `import m "github.com/grafana/grafana/pkg/models"`.