Removed experimentalFeaturesEnabled from bicepconfig.json created by rad init (#11651)

This pull request makes a small change to the Bicep configuration
template in `application.go`. The main update is the removal of the
`experimentalFeaturesEnabled` section, which previously enabled the
`extensibility` feature. This simplifies the configuration and may
indicate that the feature is no longer needed or is now enabled by
default.# Description

## Type of change

- This pull request is a minor refactor, code cleanup, test improvement,
or other maintenance task and doesn't change the functionality of Radius
(issue link optional).

## Contributor checklist
Please verify that the PR meets the following requirements, where
applicable:

- An overview of proposed schema changes is included in a linked GitHub
issue.
    - [ ] Yes <!-- TaskRadio schema -->
    - [X] Not applicable <!-- TaskRadio schema -->
- A design document PR is created in the [design-notes
repository](https://github.com/radius-project/design-notes/), if new
APIs are being introduced.
    - [ ] Yes <!-- TaskRadio design-pr -->
    - [X] Not applicable <!-- TaskRadio design-pr -->
- The design document has been reviewed and approved by Radius
maintainers/approvers.
    - [ ] Yes <!-- TaskRadio design-review -->
    - [X] Not applicable <!-- TaskRadio design-review -->
- A PR for the [samples
repository](https://github.com/radius-project/samples) is created, if
existing samples are affected by the changes in this PR.
    - [ ] Yes <!-- TaskRadio samples-pr -->
    - [X] Not applicable <!-- TaskRadio samples-pr -->
- A PR for the [documentation
repository](https://github.com/radius-project/docs) is created, if the
changes in this PR affect the documentation or any user facing updates
are made.
    - [ ] Yes <!-- TaskRadio docs-pr -->
    - [X] Not applicable <!-- TaskRadio docs-pr -->
- A PR for the [recipes
repository](https://github.com/radius-project/recipes) is created, if
existing recipes are affected by the changes in this PR.
    - [ ] Yes <!-- TaskRadio recipes-pr -->
    - [X] Not applicable <!-- TaskRadio recipes-pr -->

Signed-off-by: Zach Casper <zachcasper@microsoft.com>
Co-authored-by: Brooke Hamilton <45323234+brooke-hamilton@users.noreply.github.com>

Author: zachcasper

pkg/cli/setup/application.go

@@ -51,9 +51,6 @@ resource demo 'Applications.Core/containers@2023-10-01-preview' = {
 ` // Trailing newline intentional.
 
 	bicepConfigTemplate = `{
-	"experimentalFeaturesEnabled": {
-		"extensibility": true
-	},
 	"extensions": {
 		"radius": "br:biceptypes.azurecr.io/radius:%s",
 		"radiusCompute": "br:biceptypes.azurecr.io/radiuscompute:%s",