RFR: 8352731: Compiler workaround to forcibly set "-Xlint:-options" can be removed

[Archie Cobbs]

Back in 2011, in order to prevent repeated warnings about bootclasspath not being set ([JDK-7022337](https://bugs.openjdk.org/browse/JDK-7022337)), code was added to `JavaCompiler.java` to forcibly set the `-Xlint:-options` flag after compiler startup:

        // forcibly set the equivalent of -Xlint:-options, so that no further
        // warnings about command line options are generated from this point on
        options.put(XLINT_CUSTOM.primaryName + "-" + LintCategory.OPTIONS.option, "true");
        options.remove(XLINT_CUSTOM.primaryName + LintCategory.OPTIONS.option);

This workaround complicates logic relating to warnings in the `"options"` category and, due to improvements to the compiler design since then, it's no longer needed to actually fix the problem. So it can be removed.

As a separate cleanup, the field `optionsCheckingInitiallyDisabled` in `JavaCompiler.java` is no longer used and so it can also be removed.

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Commit messages:
 - Remove unused code.

Changes: https://git.openjdk.org/jdk/pull/24309/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=24309&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8352731
  Stats: 15 lines in 1 file changed: 0 ins; 15 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/24309.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/24309/head:pull/24309

PR: https://git.openjdk.org/jdk/pull/24309