UI: Revert api service use for requests to sys/internal/ui/mounts

[hellobontempo]

Description

✅ enterprise tests pass

The new api service automatically camelizes the keys of the response params when it returns the server data.
This is fine for parameters that were previously ember data model attributes because we often referenced those as camel cased variables.

However, for items that are actual mount paths (like secret engines or auth methods) this actually changes the value of the path. It doesn't seem to normalize dasherized paths, but if a mount is snake-cased then it camelizes it which changes the original value. This PR reverts the use of the api service for internalUiListEnabledVisibleMounts until we've decided how to handle this in the service itself.

Actual API response

{
    "auth": {
        "oidc_test/": {
            "description": "",
            "options": {},
            "type": "oidc"
        }
    },
    "secret": {}
}

data returned from api service, notice how oidc_test/ is now oidcTest/

{
    "auth": {
        "oidcTest/": {
            "description": "",
            "options": {},
            "type": "oidc"
        }
    },
    "secret": {}
}

TODO only if you're a HashiCorp employee

• Backport Labels: If this fix needs to be backported, use the appropriate backport/ label that matches the desired release branch. Note that in the CE repo, the latest release branch will look like backport/x.x.x, but older release branches will be backport/ent/x.x.x+ent.
  • LTS: If this fixes a critical security vulnerability or severity 1 bug, it will also need to be backported to the current LTS versions of Vault. To ensure this, use all available enterprise labels.
• ENT Breakage: If this PR either 1) removes a public function OR 2) changes the signature
  of a public function, even if that change is in a CE file, double check that
  applying the patch for this PR to the ENT repo and running tests doesn't
  break any tests. Sometimes ENT only tests rely on public functions in CE
  files.
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  in the PR description, commit message, or branch name.
• RFC: If this change has an associated RFC, please link it in the description.
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  description. Also, make sure the changelog is in this PR, not in your ENT PR.

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CI Results:
All Go tests succeeded! ✅

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Build Results:
All builds succeeded! ✅