Remove empty DO statement

[dkarfa]

Found empty DO statement for WP Block Parser

[ocean90]

WP Block Parser is part of the ​@wordpress/block-serialization-default-parser package. Please submit any changes at ​https://github.com/WordPress/gutenberg first. Thank you!

From a quick look, your patch will break processing the tokens.

[SergeyBiryukov]

Although the loop itself is empty, repeatedly calling $this->proceed() is important here and cannot be removed.