Remove libwebp from decoding path

[jiska2342]

• I have searched open and closed issues for duplicates
• I am submitting a bug report for existing functionality that does not work as intended
• This isn't a feature request or a discussion topic

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Bug description

Signal for iOS still depends on libwebp. Since iOS 14, WebP decoding is natively supported [1], and the minimum deployment target for Signal for iOS is iOS 15. This makes the fallback in the function runLaunchTasksIfNeededAndReloadCaches obsolete. libwebp's decoder SDImageWebPCoder is no longer needed, as Apple's decoder SDImageAWebPCoder fully replaces it for all supported iOS versions.

[1] https://developer.apple.com/documentation/safari-release-notes/safari-14-release-notes (Safari 14 changes also apply to iOS 14)

remove-libwebp-decoder.patch