RFR: 8292777: Remove hashtable.hpp from dependencies.hpp

[Coleen Phillimore]

Please review this trivial change.  Ran tier1 on 4 platforms to verify that this file isn't needed as a transitive include.

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Commit messages:
 - 8292777: Remove hashtable.hpp from dependencies.hpp

Changes: https://git.openjdk.org/jdk/pull/9979/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=9979&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8292777
  Stats: 2 lines in 1 file changed: 0 ins; 1 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/9979.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/9979/head:pull/9979

PR: https://git.openjdk.org/jdk/pull/9979