ios/Podfile: Follow {flipper -> react_native}_post_install rename.

Done to follow the template-app changes in
facebook/react-native@5c09b3fb5 and facebook/react-native@ed237b479.

Done after the RN v0.64 upgrade because the new code depends on
changes to internal RN code (scripts/react_native_pods.rb).

The two names refer to two different functions, and
react_native_post_install is new in RN v0.64. That function calls
flipper_post_install (if we've enabled Flipper by calling
`use_flipper!`, that is), and it does some other stuff. That other
stuff includes some changes to our project.pbxproj, apparently.

Author: chrisbobbe

ios/Podfile

@@ -18,10 +18,11 @@ target 'ZulipMobile' do
   # Enables Flipper.
   #
   # Note that if you have use_frameworks! enabled, Flipper will not work and
-  # you should disable these next few lines.
+  # you should disable the next line.
   use_flipper!()
+
   post_install do |installer|
-    flipper_post_install(installer)
+    react_native_post_install(installer)
   end
 
   # unimodules provides Expo packages individually.

ios/Podfile.lock

@@ -712,6 +712,6 @@ SPEC CHECKSUMS:
   Yoga: 575c581c63e0d35c9a83f4b46d01d63abc1100ac
   YogaKit: f782866e155069a2cca2517aafea43200b01fd5a
 
-PODFILE CHECKSUM: 9fe222ff44850b658732e6016d8198adb2fef518
+PODFILE CHECKSUM: d654ed98ab31318f9ce195dc15a1148e60c2d4e9
 
 COCOAPODS: 1.10.1

ios/ZulipMobile.xcodeproj/project.pbxproj

@@ -462,6 +462,7 @@
 				COPY_PHASE_STRIP = NO;
 				ENABLE_STRICT_OBJC_MSGSEND = YES;
 				ENABLE_TESTABILITY = YES;
+				"EXCLUDED_ARCHS[sdk=iphonesimulator*]" = "arm64 ";
 				GCC_C_LANGUAGE_STANDARD = gnu99;
 				GCC_DYNAMIC_NO_PIC = NO;
 				GCC_NO_COMMON_BLOCKS = YES;
@@ -528,6 +529,7 @@
 				COPY_PHASE_STRIP = YES;
 				ENABLE_NS_ASSERTIONS = NO;
 				ENABLE_STRICT_OBJC_MSGSEND = YES;
+				"EXCLUDED_ARCHS[sdk=iphonesimulator*]" = "arm64 ";
 				GCC_C_LANGUAGE_STANDARD = gnu99;
 				GCC_NO_COMMON_BLOCKS = YES;
 				GCC_WARN_64_TO_32_BIT_CONVERSION = YES;