RFR: 8239927: Product variable PrefetchFieldsAhead is unused and should be removed [v3]

[Bhavana-Kilambi]

> The product variable "PrefetchFieldsAhead" is defined in gc_globals.hpp and set in vm_version_x86.cpp. 
> But as it's not used anywhere, removing this option from the JDK source.

Bhavana-Kilambi has refreshed the contents of this pull request, and previous commits have been removed. The incremental views will show differences compared to the previous content of the PR. The pull request contains one new commit since the last revision:

  8239927: Product variable PrefetchFieldsAhead is unused and should be removed

-------------

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/6783/files
  - new: https://git.openjdk.java.net/jdk/pull/6783/files/ec81c677..bd81befb

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=6783&range=02
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=6783&range=01-02

  Stats: 2 lines in 1 file changed: 1 ins; 1 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6783.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6783/head:pull/6783

PR: https://git.openjdk.java.net/jdk/pull/6783