Promote enableFunctionCallSignatureOptimizations to stable (remove flag)

Per title, this feature flag is enabled everywhere and is clearly stable, let's 
promote to stable and remove the flag to simplify.

compiler/apps/playground/components/Editor/index.tsx

@@ -116,7 +116,6 @@ function parsePragma(pragma: string) {
   let enableEmitFreeze = null;
   let inlineUseMemo = true;
   let validateHooksUsage = true;
-  let enableFunctionCallSignatureOptimizations = true;
   let validateFrozenLambdas = true;
   let assertValidMutableRanges = true;
 
@@ -141,9 +140,6 @@ function parsePragma(pragma: string) {
   if (pragma.includes("@inlineUseMemo false")) {
     inlineUseMemo = false;
   }
-  if (pragma.includes("@enableFunctionCallSignatureOptimizations false")) {
-    enableFunctionCallSignatureOptimizations = false;
-  }
   if (pragma.includes("@validateHooksUsage false")) {
     validateHooksUsage = false;
   }
@@ -156,7 +152,6 @@ function parsePragma(pragma: string) {
 
   return {
     enableAssumeHooksFollowRulesOfReact,
-    enableFunctionCallSignatureOptimizations,
     disableAllMemoization,
     inlineUseMemo,
     memoizeJsxElements,

compiler/packages/babel-plugin-react-forget/src/HIR/Environment.ts

@@ -140,13 +140,6 @@ export type EnvironmentConfig = {
    */
   inlineUseMemo: boolean;
 
-  /**
-   * Enable optimizations based on the signature of (non-method) built-in function calls.
-   *
-   * Defaults to false
-   */
-  enableFunctionCallSignatureOptimizations: boolean;
-
   /**
    * Enable optimizations based on the `noAlias` flag of method signatures. When enabled,
    * function signatures can declare that they do not alias their arguments, allowing
@@ -240,7 +233,6 @@ const DEFAULT_ENVIRONMENT_CONFIG: Readonly<EnvironmentConfig> = {
   customHooks: null,
 
   memoizeJsxElements: true,
-  enableFunctionCallSignatureOptimizations: true,
   inlineUseMemo: true,
   validateHooksUsage: true,
   enableNoAliasOptimizations: true,

compiler/packages/babel-plugin-react-forget/src/Inference/InferReferenceEffects.ts

@@ -742,15 +742,10 @@ function inferBlock(
         continue;
       }
       case "CallExpression": {
-        let signature = getFunctionCallSignature(
+        const signature = getFunctionCallSignature(
           env,
           instrValue.callee.identifier.type
         );
-        signature =
-          env.config.enableFunctionCallSignatureOptimizations ||
-          signature?.hookKind != null
-            ? signature
-            : null;
 
         const effects =
           signature !== null ? getFunctionEffects(instrValue, signature) : null;

compiler/packages/babel-plugin-react-forget/src/ReactiveScopes/InferReactiveScopeVariables.ts

@@ -250,10 +250,7 @@ function mayAllocate(env: Environment, instruction: Instruction): boolean {
     }
     case "CallExpression":
     case "MethodCall": {
-      if (env.config.enableFunctionCallSignatureOptimizations) {
-        return instruction.lvalue.identifier.type.kind !== "Primitive";
-      }
-      return true;
+      return instruction.lvalue.identifier.type.kind !== "Primitive";
     }
     case "RegExpLiteral":
     case "PropertyStore":