Remove obsolete mode configuration and instruction files

- Deleted 3_mode_configuration_patterns.xml, which contained definitions for various mode types and their characteristics.
- Removed 4_instruction_file_templates.xml, which provided templates for creating XML instruction files for modes.
- Eliminated 5_complete_mode_examples.xml, which included canonical examples for mode creation and editing.
- Deleted 6_mode_testing_validation.xml, outlining guidelines for testing and validating modes.
- Removed 7_validation_cohesion_checking.xml, which contained principles for validating mode changes for cohesion and consistency.
- Deleted 8_global_modes.xml, documenting the workings of global modes and their interaction with workspace modes.
- Updated .roomodes to remove the mode-writer entry, which defined a mode for creating and editing custom modes.

Author: hannesrudolph