Remove Deprecated annotation for stream(V key) (#368)

* Remove Deprecated annotation for stream(V key) which was meant to be undeprecated with https://github.com/NYTimes/Store/pull/252.

* Fix CI - remove https://plugins.gradle.org/m2 repository applied to all projects.

buildsystem/dependencies.gradle

@@ -1,10 +1,6 @@
 allprojects {
     repositories {
         mavenLocal()
-        maven {
-            url 'https://plugins.gradle.org/m2/'
-        }
-
         maven {
             url = 'https://oss.sonatype.org/service/local/staging/deploy/maven2/'
         }

store/src/main/java/com/nytimes/android/external/store3/base/impl/Store.java

@@ -69,7 +69,6 @@ public interface Store<T, V> {
      * Errors will be dropped
      *
      */
-    @Deprecated
     @Nonnull
     Observable<T> stream(V key);