Remove deprecated FANTOM_ENABLE_CPP_DEBUGGING environment variable (#57401)

Summary:
Pull Request resolved: #57401

The `FANTOM_ENABLE_CPP_DEBUGGING` environment variable was kept only as a legacy alias for `FANTOM_DEBUG_CPP`. Remove it from Fantom so `FANTOM_DEBUG_CPP` is the single supported way to enable the C++ debugger.

Changelog: [Internal]

Reviewed By: sammy-SC

Differential Revision: D110324557

fbshipit-source-id: 2cbde4736137db792b8b99d1806c146e3094ca4b

Author: rubennorte

private/react-native-fantom/runner/EnvironmentOptions.js

@@ -12,7 +12,6 @@ const VALID_ENVIRONMENT_VARIABLES = [
   'FANTOM_DEBUG_CPP',
   'FANTOM_ENABLE_ASAN',
   'FANTOM_ENABLE_TSAN',
-  'FANTOM_ENABLE_CPP_DEBUGGING',
   'FANTOM_FORCE_CI_MODE',
   'FANTOM_FORCE_OSS_BUILD',
   'FANTOM_RUN_BENCHMARKS',
@@ -37,10 +36,7 @@ export const logCommands: boolean = Boolean(process.env.FANTOM_LOG_COMMANDS);
 /**
  * Enables the C++ debugger for the current test run.
  */
-export const debugCpp: boolean =
-  Boolean(process.env.FANTOM_DEBUG_CPP) ||
-  // Legacy
-  Boolean(process.env.FANTOM_ENABLE_CPP_DEBUGGING);
+export const debugCpp: boolean = Boolean(process.env.FANTOM_DEBUG_CPP);
 
 /**
  * Indicates if the current test run is done in an OSS environment (as opposed