Remove unnecessary ndk version indirection (#4755)

Summary:
[android] Remove unnecessary ndk version indirection
The constant was only referenced in one place, the ext property everywhere else.

Pull Request resolved: https://github.com/facebook/flipper/pull/4755

Test Plan:
CI

 ---
Stack created with [Sapling](https://sapling-scm.com). Best reviewed with [ReviewStack](https://reviewstack.dev/facebook/flipper/pull/4755).
* https://github.com/facebook/flipper/issues/4759
* https://github.com/facebook/flipper/issues/4758
* https://github.com/facebook/flipper/issues/4757
* https://github.com/facebook/flipper/issues/4756
* __->__ https://github.com/facebook/flipper/issues/4755
* https://github.com/facebook/flipper/issues/4754
* https://github.com/facebook/flipper/issues/4753
* https://github.com/facebook/flipper/issues/4752
* https://github.com/facebook/flipper/issues/4751

Reviewed By: ivanmisuno

Differential Revision: D46068954

Pulled By: passy

fbshipit-source-id: 276e4ee3d52a4a21c6dc29c17b6b2bd9968e945b

build.gradle

@@ -49,7 +49,7 @@ ext {
     targetSdkVersion = 31
     compileSdkVersion = 31
     buildToolsVersion = "30.0.3"
-    ndkVersion = "$NDK_VERSION"
+    ndkVersion = "25.1.8937393"
     javaTargetVersion = JavaVersion.VERSION_17
 }
 

gradle.properties

@@ -22,8 +22,6 @@ ANDROIDX_VERSION=1.3.0
 KOTLIN_VERSION=1.8.20
 FBJNI_VERSION=0.3.0
 SOLOADER_VERSION=0.10.4
-# NDK
-NDK_VERSION=25.1.8937393
 # Gradle internals
 org.gradle.internal.repository.max.retries=10
 org.gradle.internal.repository.initial.backoff=1250