Remove unused privateConcurrentReactEnabled field (#56904)

Summary:
Pull Request resolved: #56904

Remove dead code that assigned to `privateConcurrentReactEnabled` since the public getter unconditionally returns `true`. This mirrors the cleanup already done for `privateFabricEnabled` in a previous diff.

Changelog: [Internal]

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overriding_review_checks_triggers_an_audit_and_retroactive_review
Oncall Short Name: react_native_iroc

Differential Revision: D105812201

fbshipit-source-id: ca35e0029a13464096444825ca0e0f4c49a31037

Author: javache

packages/react-native/ReactAndroid/src/main/java/com/facebook/react/defaults/DefaultNewArchitectureEntryPoint.kt

@@ -103,7 +103,6 @@ public object DefaultNewArchitectureEntryPoint {
     }
 
     privateTurboModulesEnabled = turboModulesEnabled
-    privateConcurrentReactEnabled = fabricEnabled
     privateBridgelessEnabled = bridgelessEnabled
 
     DefaultSoLoader.maybeLoadSoLibrary()
@@ -139,8 +138,6 @@ public object DefaultNewArchitectureEntryPoint {
   public val turboModulesEnabled: Boolean
     get() = privateTurboModulesEnabled
 
-  private var privateConcurrentReactEnabled: Boolean = false
-
   @JvmStatic
   public val concurrentReactEnabled: Boolean
     get() = true