fix(csharp): fix lint issues - trailing whitespace, license headers, remove scratch files

- Remove scratch/design docs not meant for PR (PHASE1_TEST_RESULTS.md,
  TELEMETRY_TIMING_ISSUE.md, fix-telemetry-gaps-design.md)
- Remove accidentally committed backup file (DatabricksConnection.cs.backup)
- Fix trailing whitespace in test and doc files
- Fix license header in ChunkMetrics.cs (was using "modified" header for new file)

Co-authored-by: Isaac

Author: Jade Wang