Remove dead code found by deadcode analyzer

- Removed 5 unreachable functions (~200 LOC)
- computeIssueContentHash, shouldSkipExport from autoflush.go
- addDependencyUnchecked, removeDependencyIfExists from dependencies.go
- isUniqueConstraintError alias from util.go
- All tests still pass
- Closes bd-7c5915ae

internal/storage/sqlite/util.go

@@ -48,7 +48,4 @@ func IsUniqueConstraintError(err error) bool {
 	return strings.Contains(err.Error(), "UNIQUE constraint failed")
 }
 
-// isUniqueConstraintError is an alias for IsUniqueConstraintError for internal use
-func isUniqueConstraintError(err error) bool {
-	return IsUniqueConstraintError(err)
-}
+