[hle/services/ssl] Remove deprecated SecureTransport and SChannel backends (#4392)

Removes deprecated SecureTransport and SChannel backends, they're dead code.

See discussion on #4271

Signed-off-by: lizzie <lizzie@eden-emu.dev>

- [x] I have read and followed the [Contribution Guidelines](https://git.eden-emu.dev/eden-emu/eden/src/branch/master/CONTRIBUTING.md#code-contributions).
- [x] I have read and followed the [AI Policy](https://git.eden-emu.dev/eden-emu/eden/src/branch/master/docs/policies/AI.md)
- [x] I have read and followed the [Coding Guidelines](https://git.eden-emu.dev/eden-emu/eden/src/branch/master/docs/policies/Coding.md) to the best of my ability.

-------------------

Reviewed-on: https://git.eden-emu.dev/eden-emu/eden/pulls/4392
Reviewed-by: MaranBr <maranbr@eden-emu.dev>
Reviewed-by: crueter <crueter@eden-emu.dev>

src/core/CMakeLists.txt

@@ -1261,23 +1261,11 @@ if (ARCHITECTURE_x86_64 OR ARCHITECTURE_arm64 OR ARCHITECTURE_riscv64 OR ARCHITE
     target_link_libraries(core PRIVATE dynarmic::dynarmic)
 endif()
 
-target_sources(core PRIVATE hle/service/ssl/ssl_backend_openssl.cpp)
-
-target_link_libraries(core PRIVATE OpenSSL::SSL OpenSSL::Crypto)
-
-# TODO
-
-# elseif (APPLE)
-#     target_sources(core PRIVATE
-#         hle/service/ssl/ssl_backend_securetransport.cpp)
-#     target_link_libraries(core PRIVATE "-framework Security")
-# elseif (WIN32)
-#     target_sources(core PRIVATE
-#         hle/service/ssl/ssl_backend_schannel.cpp)
-#     target_link_libraries(core PRIVATE crypt32 secur32)
-# else()
-#     target_sources(core PRIVATE
-#         hle/service/ssl/ssl_backend_none.cpp)
-# endif()
+if (TARGET OpenSSL::SSL)
+    target_sources(core PRIVATE hle/service/ssl/ssl_backend_openssl.cpp)
+    target_link_libraries(core PRIVATE OpenSSL::SSL OpenSSL::Crypto)
+else()
+    target_sources(core PRIVATE hle/service/ssl/ssl_backend_none.cpp)
+endif()
 
 create_target_directory_groups(core)