refactor: remove a deprecated KhaosDatabase overload and unused imports

[SeriousCoding789]

What does this PR do?

• Remove KhaosDatabase.getBranch(BlockId, BlockId), which is marked @Deprecated and has no callers. getBranch(Sha256Hash, Sha256Hash), which Manager uses, is unchanged.
• Remove the 74 unused imports in production code (src/main/java): chainbase 36, framework 29, consensus 4, p2p 3, crypto 1, plugins 1. Each module is a separate commit.

Why are these changes required?

• The overload is dead code, and it behaves differently from the remaining one: it returns empty branches when a block is not in the fork database, where getBranch(Sha256Hash, Sha256Hash) throws NonCommonBlockException. The existing call sites pass a Sha256Hash as one of the two arguments, so they already resolve to the remaining overload and keep their behavior.
• The Checkstyle configuration has no UnusedImports rule, and chainbase, consensus, crypto and p2p do not run Checkstyle, so unused imports were never reported.

This PR has been tested by:

• Unit Tests: main and test code of every module compile; KhaosDatabaseTest, ManagerMockTest and checkstyle (framework, plugins) pass.
• The imports were found by scanning every tracked src/main/java file for imports whose name is not used outside comments and string literals. Imports referenced only from Javadoc {@link} are kept (UnsignedBytes in FastByteComparisons, AccountIdIndexStore in MigrateTurkishKeyHelper).

Follow up

None.

Extra details

• No behavior change: apart from the removed overload, only import lines are deleted.
• Split out of fix: harden start.sh #7003.