Fix warnings about redefined methods on AttributeTranslator

[samsonjs]

This fixes warnings about redefined attribute readers for AttributeTranslator#requirements and #request_method. The attr_reader call is redundant because those accessors are defined dynamically below that.

/Users/samsonjs/.rbenv/versions/2.6.6/lib/ruby/gems/2.6.0/gems/grape-1.5.0/lib/grape/router/attribute_translator.rb:31: warning: method redefined; discarding old requirements
/Users/samsonjs/.rbenv/versions/2.6.6/lib/ruby/gems/2.6.0/gems/grape-1.5.0/lib/grape/router/attribute_translator.rb:31: warning: method redefined; discarding old request_method

[grape-bot]

	1 Warning
⚠️	There’re library changes, but not tests. That’s OK as long as you’re refactoring existing code.

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