RFR: 8280457: Duplicate implementaion of dprecision_rounding and dstore_rounding

[Jie Fu]

Hi all,

`GraphKit::dprecision_rounding` and `GraphKit::dstore_rounding` are duplicate.
It would be better to remove one of them.

The patch removes `GraphKit::dstore_rounding` and replaces all the usages with `GraphKit::dprecision_rounding`.

Thanks.
Best regards,
Jie

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Commit messages:
 - 8280457: Duplicate implementaion of dprecision_rounding and dstore_rounding

Changes: https://git.openjdk.java.net/jdk/pull/7176/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=7176&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8280457
  Stats: 28 lines in 4 files changed: 0 ins; 17 del; 11 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7176.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7176/head:pull/7176

PR: https://git.openjdk.java.net/jdk/pull/7176