[bugfix] Remove errant alsoKnownAs inline @context entry (#4280)

# Description

> If this is a code change, please include a summary of what you've coded, and link to the issue(s) it closes/implements.
>
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Our extra `alsoKnownAs` inline `@context` entry was incorrect, and doesn't need to be included anyways as it's already present at the AS namespace context doc here: https://www.w3.org/ns/activitystreams. This PR just removes it :)

closes https://codeberg.org/superseriousbusiness/gotosocial/issues/3883

## Checklist

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- [x] I/we have discussed the proposed changes already, either in an issue on the repository, or in the Matrix chat.
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- [ ] I/we have commented the added code, particularly in hard-to-understand areas.
- [ ] I/we have made any necessary changes to documentation.
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Reviewed-on: https://codeberg.org/superseriousbusiness/gotosocial/pulls/4280
Co-authored-by: tobi <tobi.smethurst@protonmail.com>
Co-committed-by: tobi <tobi.smethurst@protonmail.com>

internal/typeutils/internaltoas_test.go

@@ -259,7 +259,6 @@ func (suite *InternalToASTestSuite) TestAccountToASAliasedAndMoved() {
     "https://w3id.org/security/v1",
     "https://www.w3.org/ns/activitystreams",
     {
-      "alsoKnownAs": "as:alsoKnownAs",
       "discoverable": "toot:discoverable",
       "featured": {
         "@id": "toot:featured",