chore: [java] synthtool not to create an initial gitignore. (#1672)

[gcf-owl-bot[bot]]

• chore: [java] synthtool not to create an initial gitignore.

Given that new generated libraries will come to the Java monorepo going forward and that any new hand-written libraries can get a new .gitignore from humans, there's no need to automatically prepare .gitignore file.

• deleting gitignore

• deleting .gitignore from golden Source-Link: https://github.com/googleapis/synthtool/commit/0baf7e4b652fcc7bf77ec341965c62c0b67e722d Post-Processor: gcr.io/cloud-devrel-public-resources/owlbot-java:latest@sha256:25a679b48797fcdd98fe339c885d9595a8be5c16a275d1b466ba98e6951a3217

[gcf-merge-on-green[bot]]

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