Revert "Make r25.2.3 the default Android SDK"

This reverts commit a9e75da. `./mach build --android --dev` does not work with SDK 25.2.3. SDK 25.2.3 is still available for the `./mach package step`.
servo · aneeshusa · May 8, 2017 · May 8, 2017 · b8cdea03da78bb050b57c17905e77ef9e88c8443
commit b8cdea03da78bb050b57c17905e77ef9e88c8443
diff --git a/servo-build-dependencies/map.jinja b/servo-build-dependencies/map.jinja
@@ -1,7 +1,12 @@
 {%
   set android = {
     'sdk': {
-      'current': 'r25.2.3',
+      'current': 'r24.4.1',
+      'r24.4.1': {
+        'build_tools': '23.0.3',
+        'platform': '18',
+        'sha512': '778f43ab1d220bdc30087759862d2c0f3fa59e44122cc99666d57f37f69d46b14e4b8583e20234e23aaed4e291f5a21e607d08f69a2a9e73332889091054b8c9',
+      },
       'r25.2.3': {
         'build_tools': '25.0.2',
         'platform': '25',