RFR: 8368975: Windows ProcessImpl.java has dead code

[Francesco Andreuzzi]

Removal of dead code in the windows flavor of `ProcessImpl.java`. The removed branches can't be reached because `allowAmbiguousCommands` is known to be `false` in the `else` block.

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Commit messages:
 - remove dead code

Changes: https://git.openjdk.org/jdk/pull/27945/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=27945&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8368975
  Stats: 7 lines in 1 file changed: 0 ins; 3 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/27945.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27945/head:pull/27945

PR: https://git.openjdk.org/jdk/pull/27945