Remove prerelease abseil code (#558)

* Add abseil bits to the iOS build

* Migrate from prerelease to published abseil bits in ordered_code

* Remove prerelease abseil code

Author: wilhuff

FirebaseFirestore.podspec

@@ -33,7 +33,8 @@ Google Cloud Firestore is a NoSQL document database built for automatic scaling,
     'Firestore/Port/**/*',
     'Firestore/Protos/objc/**/*.[hm]',
     'Firestore/core/src/**/*.{h,cc}',
-    'Firestore/third_party/Immutable/*.[mh]'
+    'Firestore/third_party/Immutable/*.[mh]',
+    'Firestore/third_party/abseil-cpp/absl/*.{h,cc}'
   ]
   s.requires_arc = [
     'Firestore/Source/**/*',
@@ -54,9 +55,10 @@ Google Cloud Firestore is a NoSQL document database built for automatic scaling,
   s.frameworks = 'MobileCoreServices'
   s.library = 'c++'
   s.pod_target_xcconfig = {
-    'GCC_PREPROCESSOR_DEFINITIONS' =>
-      'GPB_USE_PROTOBUF_FRAMEWORK_IMPORTS=1 ',
-      'HEADER_SEARCH_PATHS' => '"${PODS_TARGET_SRCROOT}"',
-      'OTHER_CFLAGS' => '-DFIRFirestore_VERSION=' + s.version.to_s
+    'GCC_PREPROCESSOR_DEFINITIONS' => 'GPB_USE_PROTOBUF_FRAMEWORK_IMPORTS=1 ',
+    'HEADER_SEARCH_PATHS' =>
+      '"${PODS_TARGET_SRCROOT}" ' +
+      '"${PODS_TARGET_SRCROOT}/Firestore/third_party/abseil-cpp"',
+    'OTHER_CFLAGS' => '-DFIRFirestore_VERSION=' + s.version.to_s
   }
 end