RFR: 8253889: Remove ExecMem constant

[Thomas Stuefe]

Hi,

may I have reviews please for this trivial cleanup.

ExecMem is defined in os.hpp as:

// Executable parameter flag for os::commit_memory() and
// os::commit_memory_or_exit().
const bool ExecMem = true;

and only ever used as "!ExecMem" parameter value to the "executable" argument in calls to os::commit_memory().

Maybe it did something in the past. Now it just seems to be a complicated way to say "false".

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Commit messages:
 - initial commit

Changes: https://git.openjdk.java.net/jdk/pull/454/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=454&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8253889
  Stats: 26 lines in 13 files changed: 0 ins; 4 del; 22 mod
  Patch: https://git.openjdk.java.net/jdk/pull/454.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/454/head:pull/454

PR: https://git.openjdk.java.net/jdk/pull/454