Revert "Start diagnostic group_id at 1 to handle non LS diagnostics (#22694) (#22700)

This reverts commit 3ae6aa0e4d.

If "group_id = 0" really did mean a diagnostic not from a language
server then various methods related to diagnostic set would need to be
updated. Something like [this
diff](https://gist.github.com/mgsloan/e902153bcaec207b39260a8f40d3134d).

Plan instead is to use InfoPopover instead of DiagnosticPopover for
these.

Release Notes:

- N/A

crates/collab/src/tests/integration_tests.rs

@@ -4065,7 +4065,7 @@ async fn test_collaborating_with_diagnostics(
                 DiagnosticEntry {
                     range: Point::new(0, 4)..Point::new(0, 7),
                     diagnostic: Diagnostic {
-                        group_id: 3,
+                        group_id: 2,
                         message: "message 1".to_string(),
                         severity: lsp::DiagnosticSeverity::ERROR,
                         is_primary: true,
@@ -4075,7 +4075,7 @@ async fn test_collaborating_with_diagnostics(
                 DiagnosticEntry {
                     range: Point::new(0, 10)..Point::new(0, 13),
                     diagnostic: Diagnostic {
-                        group_id: 4,
+                        group_id: 3,
                         severity: lsp::DiagnosticSeverity::WARNING,
                         message: "message 2".to_string(),
                         is_primary: true,