Revert "Update headers to track vertex ai/developer usage in kotlin (#6944)"

This reverts commit f4649cd.

Author: daymxn

firebase-vertexai/src/main/kotlin/com/google/firebase/vertexai/GenerativeModel.kt

@@ -84,7 +84,7 @@ internal constructor(
       apiKey,
       modelName,
       requestOptions,
-      "gl-kotlin/${KotlinVersion.CURRENT}-ai fire/${BuildConfig.VERSION_NAME}",
+      "gl-kotlin/${KotlinVersion.CURRENT} fire/${BuildConfig.VERSION_NAME}",
       firebaseApp,
       AppCheckHeaderProvider(TAG, appCheckTokenProvider, internalAuthProvider),
     ),

firebase-vertexai/src/main/kotlin/com/google/firebase/vertexai/ImagenModel.kt

@@ -65,7 +65,7 @@ internal constructor(
       apiKey,
       modelName,
       requestOptions,
-      "gl-kotlin/${KotlinVersion.CURRENT}-ai fire/${BuildConfig.VERSION_NAME}",
+      "gl-kotlin/${KotlinVersion.CURRENT} fire/${BuildConfig.VERSION_NAME}",
       firebaseApp,
       AppCheckHeaderProvider(TAG, appCheckTokenProvider, internalAuthProvider),
     ),

firebase-vertexai/src/main/kotlin/com/google/firebase/vertexai/LiveGenerativeModel.kt

@@ -83,7 +83,7 @@ internal constructor(
       apiKey,
       modelName,
       requestOptions,
-      "gl-kotlin/${KotlinVersion.CURRENT}-ai fire/${BuildConfig.VERSION_NAME}",
+      "gl-kotlin/${KotlinVersion.CURRENT} fire/${BuildConfig.VERSION_NAME}",
       firebaseApp,
       AppCheckHeaderProvider(TAG, appCheckTokenProvider, internalAuthProvider),
     ),