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.

---
<!-- Thank you for contributing to Servo! Please replace each `[ ]` by `[X]` when the step is complete, and replace `__` with appropriate data: -->
- [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).

<!-- Either: -->
- [ ] 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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Cargo.lock

@@ -2463,7 +2463,6 @@ dependencies = [
 name = "servo"
 version = "0.0.1"
 dependencies = [
- "android_glue 0.2.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "android_injected_glue 0.2.1 (git+https://github.com/mmatyas/android-rs-injected-glue)",
  "backtrace 0.3.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "browserhtml 0.1.17 (git+https://github.com/browserhtml/browserhtml?branch=crate)",
@@ -2471,7 +2470,6 @@ dependencies = [
  "gfx_tests 0.0.1",
  "glutin_app 0.0.1",
  "layout_tests 0.0.1",
- "libc 0.2.20 (registry+https://github.com/rust-lang/crates.io-index)",
  "libservo 0.0.1",
  "log 0.3.6 (registry+https://github.com/rust-lang/crates.io-index)",
  "net_tests 0.0.1",