Remove confusing 'previously unseen snapshot' message (#812)

## Problem

When running `cargo insta test --force-update-snapshots --accept`,
existing snapshots showed:
```
created previously unseen snapshot /path/to/snapshot.snap
```

This was confusing since the snapshots weren't new - they were being
updated.

## Solution

Remove the conditional message logic and always print "updated snapshot"
for in-place updates.

## Changes

- Simplified message in `runtime.rs:558-562` to always show "updated
snapshot"
- Kept the TODO comment documenting that the `unseen` logic is inverted
(for context)
- Updated inline snapshot formatting from test runs

## Notes

The `unseen` variable still has inverted logic (`true` when file exists,
not when it doesn't), which affects the deprecated `INSTA_UPDATE=unseen`
mode. Since that mode is deprecated, we're not fixing the logic - just
removing its use in the message.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Co-authored-by: Claude <noreply@anthropic.com>

Author: max-sixty

insta/src/runtime.rs

@@ -557,11 +557,7 @@ impl<'a> SnapshotAssertionContext<'a> {
                     if should_print {
                         elog!(
                             "{} {}",
-                            if unseen {
-                                style("created previously unseen snapshot").green()
-                            } else {
-                                style("updated snapshot").green()
-                            },
+                            style("updated snapshot").green(),
                             style(snapshot_file.display()).cyan().underlined(),
                         );
                     }

insta/src/snapshot.rs

@@ -1430,11 +1430,10 @@ fn test_empty_lines() {
     multiline content starting on second line
 
     final line
-    "#, @r###"
-
-        multiline content starting on second line
+    "#, @r"
 
-        final line
+    multiline content starting on second line
 
-    "###);
+    final line
+    ");
 }

insta/tests/test_inline.rs

@@ -299,6 +299,8 @@ fn test_inline_test_in_loop() {
 #[test]
 fn test_inline_snapshot_whitespace() {
     assert_snapshot!("\n\nfoo\n\n    bar\n\n", @r"
+
+
     foo
 
         bar