Remove individual class BETA guards

Remove individual class BETA guards

Summary:
Eolian adds a per-class BETA guard (like EFL_UI_WIN_BETA) to any method tagged
as @beta. This means that any app (and the EFL code) wanting to use BETA features
has to enable them class by class, which is cumbersome.
This commit replaces the individual guards with the global EFL_BETA_API_SUPPORT
guard, so apps only need to define one symbol to access BETA features.

Any usage of the per-class guards has been removed from the EFL code and examples.
When building EFL the global guard is defined by configure, so all EFL methods
already have access to BETA API.
Efl_Core.h and Efl_Ui.h no longer define EFL_BETA_API_SUPPORT. Apps wanting to
use BETA API have to define this symbol before including any EFL header
(It has been added to the examples requiring it).

Test Plan:
make && make check && make examples still work, but there's a lot less #defines
in the code

Reviewers: zmike, bu5hm4n, q66

Reviewed By: q66

Subscribers: cedric, #reviewers, #committers

Tags: #efl

Maniphest Tasks: T6788

Differential Revision: https://phab.enlightenment.org/D7924