Remove Captin software icon (#50277)

<!-- Add the related story/sub-task/bug number, like Resolves #123, or
remove if NA -->
**Related issue:** N/A

# What this does

Removes the **Captin** software icon: the `Captin.tsx` fallback icon
component and its
`SOFTWARE_NAME_TO_ICON_MAP` entry.

Captin is deprecated and is being removed as a Fleet-maintained app. Its
manifest fails
the FMA validator because the download at the pinned URL now installs
2.0.1 while
Homebrew still declares 1.3.1:

```
level=INFO msg="Looking for app: Captin, version: 1.3.1" app=Captin
level=INFO msg="Found app: 'Captin' at /Applications/Captin.app, Version: 2.0.1, Bundled Version: 203"
level=ERROR msg="App version '1.3.1' was not found by osquery" app=Captin
```

Split out of the FMA removal so the frontend change can be reviewed on
its own.

> [!NOTE]
> **Merge order.** The FMA removal (input, output manifest, and
`apps.json` entry) is in a
> separate PR. Merging this one first leaves the Captin FMA without a
fallback icon until
> that PR lands, so it should merge after — or at the same time as — the
FMA removal.

Verified nothing else references `Captin` after the removal. The one
remaining mention in
the repo is a row in `cmd/osquery-perf/software-library/software.sql`,
which is a
load-test software inventory corpus rather than an FMA reference, so it
is left alone.

# Checklist for submitter

- [x] QA'd all new/changed functionality manually

No changes file: this is not a user-visible change on its own, and
matches how other FMA
catalog/icon PRs ship (e.g. #50028, #50024).


<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

* **Bug Fixes**
  * Removed the obsolete Captin icon from the software listings.
  * Prevented the retired icon from appearing in software name mappings.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

frontend/pages/SoftwarePage/components/icons/index.ts

@@ -165,7 +165,6 @@ import CamundaModeler from "./CamundaModeler";
 import Canva from "./Canva";
 import CapCut from "./CapCut";
 import Captain from "./Captain";
-import Captin from "./Captin";
 import Capto from "./Capto";
 import CarbonCopyCloner from "./CarbonCopyCloner";
 import Cardhop from "./Cardhop";
@@ -1315,7 +1314,6 @@ export const SOFTWARE_NAME_TO_ICON_MAP = {
   canva: Canva,
   capcut: CapCut,
   captain: Captain,
-  captin: Captin,
   capto: Capto,
   "carbon copy cloner": CarbonCopyCloner,
   cardhop: Cardhop,