Merge BlazeModule.getEnvironmentExtensions into serverInit / ServerBuilder.

--
MOS_MIGRATED_REVID=137955061
diff --git a/src/main/java/com/google/devtools/build/lib/runtime/BlazeRuntime.java b/src/main/java/com/google/devtools/build/lib/runtime/BlazeRuntime.java
index 5037ee6..61a02ab 100644
--- a/src/main/java/com/google/devtools/build/lib/runtime/BlazeRuntime.java
+++ b/src/main/java/com/google/devtools/build/lib/runtime/BlazeRuntime.java
@@ -1090,11 +1090,6 @@
 
       ConfiguredRuleClassProvider ruleClassProvider = ruleClassBuilder.build();
 
-      List<PackageFactory.EnvironmentExtension> extensions = new ArrayList<>();
-      for (BlazeModule module : blazeModules) {
-        extensions.add(module.getPackageEnvironmentExtension());
-      }
-
       Package.Builder.Helper packageBuilderHelper = null;
       for (BlazeModule module : blazeModules) {
         Package.Builder.Helper candidateHelper =
@@ -1114,7 +1109,7 @@
               ruleClassProvider,
               ruleClassBuilder.getPlatformRegexps(),
               serverBuilder.getAttributeContainerFactory(),
-              extensions,
+              serverBuilder.getEnvironmentExtensions(),
               BlazeVersionInfo.instance().getVersion(),
               packageBuilderHelper);