RFR: 8261652: Remove some dead comments from os_bsd_x86

[Vladimir Kempik]

This removes some dead comments form bsd_x86 and double include of pthread.h

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Commit messages:
 - 8261652: Remove some dead comments from os_bsd_x86

Changes: https://git.openjdk.java.net/jdk/pull/2547/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=2547&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8261652
  Stats: 11 lines in 1 file changed: 0 ins; 11 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/2547.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/2547/head:pull/2547

PR: https://git.openjdk.java.net/jdk/pull/2547