Remove developer documentation about not describing symbols

This is now covered by rubocop-rspec.

doc/development/gotchas.md

@@ -3,35 +3,6 @@
 The purpose of this guide is to document potential "gotchas" that contributors
 might encounter or should avoid during development of GitLab CE and EE.
 
-## Do not `describe` symbols
-
-Consider the following model spec:
-
-```ruby
-require 'rails_helper'
-
-describe User do
-  describe :to_param do
-    it 'converts the username to a param' do
-      user = described_class.new(username: 'John Smith')
-
-      expect(user.to_param).to eq 'john-smith'
-    end
-  end
-end
-```
-
-When run, this spec doesn't do what we might expect:
-
-```sh
-spec/models/user_spec.rb|6 error|  Failure/Error: u = described_class.new NoMethodError: undefined method `new' for :to_param:Symbol
-```
-
-### Solution
-
-Except for the top-level `describe` block, always provide a String argument to
-`describe`.
-
 ## Do not assert against the absolute value of a sequence-generated attribute
 
 Consider the following factory:

doc/development/testing.md

@@ -195,7 +195,6 @@ Please consult the [dedicated "Frontend testing" guide](./fe_guide/testing.md).
 - Use `context` to test branching logic.
 - Use multi-line `do...end` blocks for `before` and `after`, even when it would
   fit on a single line.
-- Don't `describe` symbols (see [Gotchas](gotchas.md#dont-describe-symbols)).
 - Don't assert against the absolute value of a sequence-generated attribute (see [Gotchas](gotchas.md#dont-assert-against-the-absolute-value-of-a-sequence-generated-attribute)).
 - Don't supply the `:each` argument to hooks since it's the default.
 - Prefer `not_to` to `to_not` (_this is enforced by RuboCop_).