set sdk versions per variant

Prev build will crash on android 12 because it claims to know about
sdk 31 but gets Bluetooth permissions wrong. It's been released on
fdroid due to miscommunication. Fix will be to roll non-gplay variants
back to 30 for now. I'm deliberately breaking gplay builds because
nothing should ship there until I sort out the permissions stuff 31
requires. (Shipping 30 is no longer possible for the gplay store.)

xwords4/android/app/build.gradle

@@ -80,7 +80,6 @@ android {
         } else {
             minSdkVersion 14
         }
-        targetSdkVersion 31     // must match ../build.gradle
         versionCode VERSION_CODE_BASE
         versionName VERSION_NAME
     }
@@ -152,6 +151,8 @@ android {
 
         xw4fdroid {
             dimension "variant"
+            targetSdkVersion 30
+            compileSdkVersion 30
             applicationId "org.eehouse.android.xw4"
             manifestPlaceholders = [ APP_ID: applicationId ]
             resValue "string", "app_name", "CrossWords"
@@ -168,6 +169,8 @@ android {
 
         xw4d {
             dimension "variant"
+            targetSdkVersion 30
+            compileSdkVersion 30
             buildConfigField "String", "DB_NAME", "\"xwddb\""
             applicationId "org.eehouse.android.xw4dbg"
             resValue "string", "app_name", "CrossDbg"
@@ -206,6 +209,8 @@ android {
 
         xw4Foss {
             dimension "variant"
+            targetSdkVersion 30
+            compileSdkVersion 30
             applicationId "org.eehouse.android.xw4"
             manifestPlaceholders = [ APP_ID: applicationId ]
             resValue "string", "app_name", "CrossWords"

xwords4/android/build.gradle

@@ -27,13 +27,3 @@ allprojects {
 task clean(type: Delete) {
     delete rootProject.buildDir
 }
-
-subprojects {
-    afterEvaluate {project ->
-        if (project.hasProperty("android")) {
-            android {
-                compileSdkVersion 31 // must match app/build.gradle
-            }
-        }
-    }
-}