fix(database, iOS): remove unnecessary order modifier checks in query construction

[SelaseKay]

Description

Fixes a crash on iOS when subscribing with onValue to a query that uses startAt or startAfter (including with a secondary key) without a preceding orderBy modifier (#18132).

Previously, the plugin used hasOrderModifier to special-case this scenario in queryObserve by calling queryLimited(toFirst: 0). This is not valid in the Firebase iOS SDK and triggers validateLimitRange:.

This change removes that guard. The plugin now always applies the standard queryStarting(atValue:...) or queryStarting(afterValue:...) calls, matching other query paths and allowing the native SDK to handle the query correctly.

Related Issues

Fixes #18132

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Checklist

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• I updated/added relevant documentation (doc comments with ///).
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Breaking Change

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• Yes, this is a breaking change.
• No, this is not a breaking change.

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