Remove use of Bazel's `--android_cpu` flag

*Title*: *Remove use of Bazel's `--android_cpu` flag*

*Description*:
Bazel is currently removing legacy Android flags (such as `--android_cpu`). See https://blog.bazel.build/2023/11/15/android-platforms.html for more details.

Currently, envoy's [`mobile/bazel/android_debug_info.bzl`](https://github.com/envoyproxy/envoy/blob/main/mobile/bazel/android_debug_info.bzl) is relying on this (via the `android_cfg` configuration fragment).

This flag will be gone in Bazel 8.0 (due to be released Fall 2024), at that point the code will need to be updated.

I attempted a fix in https://github.com/envoyproxy/envoy/pull/33010 but was unable to run your tests and figure out the problem with my patch. (Thanks to @abeyad for helping me debug).

As a note, by Bazel 8.0, all Android rules will be in Starlark and this may require other changes to your use of them.