Noop: Omit type annotations for local variables.

[YuzuruT]

Following the style suggestion in effective dart

omit_local_variable_types

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[YuzuruT]

@googlebot I signed it!

[sugoi-yuzuru]

The style fixes now include

1. omit_local_variable_types
2. prefer_adjacent_string_concatenation
3. always_declare_return_types
4. prefer_single_quotes
5. prefer_is_not_empty
6. prefer_contains