Delete `Mac mac_unopt > ci/ios_debug_unopt_sim`

Currently we have `Mac mac_unopt > ci/ios_debug_unopt_sim`, but we also have `Mac mac_unopt > ci/ios_debug_unopt_sim_arm64`

The non-arm version of the test verifies that an x86 build of the engine works on a simulator.

Xcode no longer supports intel simulators and is dropping Rosetta support. We should just remove this build. The x86 simulator build will still be built in `Mac mac_ios_engine > ci/ios_debug_sim`, we're just not going to test it anymore.

https://github.com/flutter/flutter/blob/1ceffd11a4714c13566358ba4a7b72b7915805bb/engine/src/flutter/ci/builders/mac_unopt.json#L266-L330