deps.ffmpeg: Remove MbedTLS CMake files from macOS FFmpeg package

[PatTheMav]

Description

Removes MbedTLS CMake package files for macOS FFmpeg builds.

Motivation and Context

Once the project switches MbedTLS 3.6+, there needs to be a way to distinguish between older and newer versions on the obs-studio side.

The path of least resistance is to use CMake package-based discovery for versions 3.6+ and find module-based discovery for older versions, which requires the older (current as of time of the commit) versions to not provide a CMake package as part of obs-deps.

Note

Once MbedTLS is updated to version 3.6+, this removal will need to be removed again.

How Has This Been Tested?

Tested removal on current obs-deps with an updated obs-studio to opportunistically use package discovery mode and observe automatic fallback to find module to discover MbedTLS as provided by current dependencies.

Types of changes

• Bug fix (non-breaking change which fixes an issue)

Checklist:

• My code has been run through clang-format.
• I have read the contributing document.
• My code is not on the master branch.
• The code has been tested.
• All commit messages are properly formatted and commits squashed where appropriate.
• I have included updates to all appropriate documentation.

[RytoEX]

Seems fine, though we'll have to remember to remove this when eventually updating mbedTLS.