[Fix #6725][Fix #6540] Mark Style/SymbolProc as unsafe for auto-correct

[Drenmi]

Marking Style/SymbolProc as unsafe for auto-correct, since there are many cases where this is unsafe.

Some examples: #6725, #6540, #6448, #6052, #5098, #5009, #3071, #2135, #2588

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Before submitting the PR make sure the following are checked:

• Wrote good commit messages.
• Commit message starts with [Fix #issue-number] (if the related issue exists).
• Feature branch is up-to-date with master (if not - rebase it).
• Squashed related commits together.
• Added tests.
• Added an entry to the Changelog if the new code introduces user-observable changes. See changelog entry format.
• The PR relates to only one subject with a clear title
  and description in grammatically correct, complete sentences.
• Run bundle exec rake default. It executes all tests and RuboCop for itself, and generates the documentation.

[koic]

Thanks for showing the example issues!

[Malabarba]

Today I just randomly found out an issue I had forgotten about has been fixed less than a month ago. Thanks for all the work and effort you all put into rubocop!