CI: Remove explicit LANGUAGE flags for cmake 3.19+

[PatTheMav]

Description

Removes the Cmake directives to explicitly set the language of some plugins to C on macOS which breaks most recent cmake versions.

Motivation and Context

Cmake merged and released a change with version 3.19 that breaks building on macOS with our current cmake rules.

The change as explained in https://gitlab.kitware.com/cmake/cmake/-/merge_requests/4780 now sets the language flag explicitly when LANGUAGE is set in cmake rules. This leads to the switch -x c being added to calls to cc or clang which then fails when the compiler meets an ObjectiveC file (as is the case in libobs and some other plugins.

According to one of cmake's maintainers, the flag is supposed to explicitly set the source code language, not which compiler is preferred. This PR removes all instances of setting the LANGUAGE for plugins that use ObjectiveC to enable compilation again.

Note that Cmake is not part of macOS default or development distribution, so it has to be installed via Homebrew where 3.19 is the default version.

How Has This Been Tested?

• OBS compiled and tested with cmake 3.19

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.