Remove bridgelessEnabled from DefaultNewArchitectureEntryPoint - #58415

Summary:
Bridgeless is the only supported mode in the New Architecture, so the
`bridgelessEnabled` flag on `DefaultNewArchitectureEntryPoint` was dead
configuration: every `load(...)` path passed `true`, and `isConfigurationValid`
raised an error when it was `false`. The entry point advertised a toggle that
could only ever hold the one value that is already mandatory.
This removes that surface from `ReactAndroid`:
- Removed the public `bridgelessEnabled` getter and its backing field.
- Removed the deprecated three-argument
 `load(turboModulesEnabled, fabricEnabled, bridgelessEnabled)` overload. Its
 implementation body moved into the two-argument overload, since dropping the
 parameter alone would have collided with the existing
 `load(Boolean, Boolean)` signature.
- Removed the `bridgelessEnabled` parameter from `isConfigurationValid`,
 reducing the guard to `!turboModulesEnabled || !fabricEnabled` and shortening
 the resulting error message.
- `loadWithFeatureFlags` no longer reads `enableBridgelessArchitecture()`.
Behavior note: `loadWithFeatureFlags` previously raised an error when a feature
flags provider returned `enableBridgelessArchitecture() == false`. That check is
gone. It was unreachable in practice because bridgeless is not optional, but it
is a removed validation rather than a pure no-op cleanup.
Bridgeless remains unconditionally enabled. Callers using the no-argument
`load()` are unaffected. The regenerated `ReactAndroid.api` drops exactly
`getBridgelessEnabled ()Z`, `load (ZZZ)V`, and
`load$default (ZZZILjava/lang/Object;)V`.
The equivalent iOS cleanup is intentionally left to a follow-up change.
Changelog:
[Android][Breaking] - Remove `DefaultNewArchitectureEntryPoint.bridgelessEnabled` and the deprecated three-argument `load(turboModulesEnabled, fabricEnabled, bridgelessEnabled)` overload; bridgeless is always enabled in the New Architecture
Differential Revision: D116317210