Revert "jni_zero: Always multiplexing when GN arg is set"

This reverts commit 90703dea1b7688b69dfcf907acf53e777ee52b76.

Reason for revert:
https://ci.chromium.org/ui/p/chromium/builders/build/android-build-perf-ninja/721/overview
```
[5269/145324] ACTION //chrome/android:libmonochrome_inputs__jni_registration(//build/toolchain/android:android_clang_arm64)
FAILED: gen/chrome/android/libmonochrome_inputs__jni_registration.srcjar
python3 ../../third_party/jni_zero/jni_zero.py generate-final --srcjar-path gen/chrome/android/libmonochrome_inputs__jni_registration.srcjar --depfile gen/chrome/android/libmonochrome_inputs__jni_registration.d --java-sources-file gen/chrome/android/libmonochrome_inputs__jni_registration.javasources.txt --native-sources-file gen/chrome/android/libmonochrome_inputs__jni_registration.nativesources.txt --priority-java-sources-file gen/chrome/android/libmonochrome_inputs__jni_registration.priority_javasources.txt
usage: jni_zero.py [-h] {from-source,from-jar,generate-final} ...
jni_zero.py: error: --priority-java-sources is only for multiplexing.
```

Original change's description:
> jni_zero: Always multiplexing when GN arg is set
>
> We had the ability to set multiplexing off on a per-target level, but we
> didn't use it, and may as well clean up unused confusing stuff if it's
> providing no value.
>
> Bug: 40612925
> Change-Id: I7f4f214c55453b1762d360466031cc787862f1a5
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5631659
> Commit-Queue: Andrew Grieve <agrieve@chromium.org>
> Auto-Submit: Sam Maier <smaier@chromium.org>
> Reviewed-by: Andrew Grieve <agrieve@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#1315002}

Bug: 40612925
Change-Id: I8da46d03db45d3ea7fe7c3b932629addc09e1a26
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5632600
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Commit-Queue: Andrew Grieve <agrieve@chromium.org>
Auto-Submit: Fumitoshi Ukai <ukai@google.com>
Reviewed-by: Andrew Grieve <agrieve@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1315185}
NOKEYCHECK=True
GitOrigin-RevId: 24d893385d9339270cec3ace5407596b8b693aa5
1 file changed