Bootstrap empty glob file

1. Initialize an empty glob file for .bootstrap/build.ninja. Initializing
in soong_ui (and not soong_build) prevents inadvertently creating the
file inside the source tree
2. Remove soong-build-globs.ninja, which is not used during the build

Bug: 187194795
Test: Ran the following command locally for the target
art-target-arm:git_master-art
```
. ./build/envsetup.sh && lunch armv8-eng &&
art/tools/buildbot-build.sh --target
```

Change-Id: Ibe6eeff65ea1ab25136642299e9878d0da1cac42