Auto merge of #15609 - fabricedesre:android-cleanup, r=Wafflespeanut

Android cleanup

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As I dive in the Android code, a bit of cleanup:
- jni/main.c was totally useless, and its presence misleading. I left the jni/ directory to please `ndk-build`.
- the logging redirection in servo/main.rs was redondant with the implementation in the injected android glue.

Most other changes are just due to my editor doing a `rustfmt` when saving files.
I also turned on RUST_LOG to `debug` by default, that helps quite a bit to see what's happening.

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- [X ] `./mach build -d` does not report any errors
- [X ] `./mach test-tidy` does not report any errors
- [ ] These changes fix #__ (github issue number if applicable).

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- [ ] There are tests for these changes OR
- [X ] These changes do not require tests because unfortunately we don't have Android tests.

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