[soheetech]

What is this PR for?

This PR refreshes legacy deployment documentation (virtual_machine.md and yarn_install.md) to resolve outdated prerequisites and deprecated repository URLs.
It explicitly frames legacy VM provisioning and Hortonworks HDP 2.3.1 setups (CentOS 6, Java 7/8, Spark 1.6, Hadoop 2.7) as historical references rather than current contributor guides, and points readers to active build guides and official GitHub repository URLs.

What type of PR is it?

Documentation

Todos

• - Mark legacy VM provisioning and the HDP 2.3.1 YARN setup as historical references
• - Clarify that the documented Java 8 and Spark 1.6 examples are not current development requirements
• - Replace the clone example with the official GitHub HTTPS URL

What is the Jira issue?

https://issues.apache.org/jira/browse/ZEPPELIN-6440

How should this be tested?

1. Verify stale references are removed or properly contextualized as historical examples via search:

   git grep -n -E "git://git.apache.org|openjdk-7-jdk|0\.12\.7|Spark 1\.6|Hadoop 2\.4" -- docs/setup/deployment/virtual_machine.md docs/setup/deployment/yarn_install.md README.md

• Confirmed git://git.apache.org is completely removed.
• Confirmed remaining Spark 1.6 references in yarn_install.md are clearly framed as historical examples.

2. Run whitespace and format validation:

git diff --check

Questions:

• Does the license files need to update? No
• Is there breaking changes for older versions? No
• Does this needs documentation? No (this PR updates documentation itself)