Spring-ai Remove deprecated output parser in favor of converters

All output parser functionality has already been migrated to the converter package since milestone M1.

Changes: - Replace all instances of 'parser' with 'converter' in variable names and test cases - Delete (pre M1) deprecated parser package and all associated classes - Remove Output Parsers section from README.md - Update Javadoc comments to reference converters instead of parsers

Comment From: ilayaperumalg

LGTM, merging after resolving the conflict.

Comment From: ilayaperumalg

Resolved the conflicts, rebased and merged as 33a7241