ios/Podfile: Use new, acceptable Flipper version defaults from RN v0.64.

These defaults are set in
  https://github.com/facebook/react-native/blob/v0.64.2/scripts/react_native_pods.rb:

  versions['Flipper'] ||= '~> 0.75.1'
  versions['Flipper-Folly'] ||= '~> 2.5.3'
  versions['Flipper-RSocket'] ||= '~> 1.3'

We started pinning to some specific versions in 912cb9e, following
published advice from RN in
facebook/react-native#31480 for fixing a
build issue with Xcode 12.5. Checking that advice again, its entry
suggests that we don't have to do anything as long as we're at RN
v0.64.1 or higher. Which makes sense, seeing those defaults.

Author: chrisbobbe

ios/Podfile

@@ -19,11 +19,7 @@ target 'ZulipMobile' do
   #
   # Note that if you have use_frameworks! enabled, Flipper will not work and
   # you should disable these next few lines.
-  use_flipper!(
-    'Flipper' => '0.75.1',
-    'Flipper-Folly' => '2.5.3',
-    'Flipper-RSocket' => '1.3.1',
-  )
+  use_flipper!()
   post_install do |installer|
     flipper_post_install(installer)
   end

ios/Podfile.lock

@@ -438,25 +438,25 @@ DEPENDENCIES:
   - EXWebBrowser (from `../node_modules/expo-web-browser/ios`)
   - FBLazyVector (from `../node_modules/react-native/Libraries/FBLazyVector`)
   - FBReactNativeSpec (from `../node_modules/react-native/React/FBReactNativeSpec`)
-  - Flipper (= 0.75.1)
+  - Flipper (~> 0.75.1)
   - Flipper-DoubleConversion (= 1.1.7)
-  - Flipper-Folly (= 2.5.3)
+  - Flipper-Folly (~> 2.5.3)
   - Flipper-Glog (= 0.3.6)
   - Flipper-PeerTalk (~> 0.0.4)
-  - Flipper-RSocket (= 1.3.1)
-  - FlipperKit (= 0.75.1)
-  - FlipperKit/Core (= 0.75.1)
-  - FlipperKit/CppBridge (= 0.75.1)
-  - FlipperKit/FBCxxFollyDynamicConvert (= 0.75.1)
-  - FlipperKit/FBDefines (= 0.75.1)
-  - FlipperKit/FKPortForwarding (= 0.75.1)
-  - FlipperKit/FlipperKitHighlightOverlay (= 0.75.1)
-  - FlipperKit/FlipperKitLayoutPlugin (= 0.75.1)
-  - FlipperKit/FlipperKitLayoutTextSearchable (= 0.75.1)
-  - FlipperKit/FlipperKitNetworkPlugin (= 0.75.1)
-  - FlipperKit/FlipperKitReactPlugin (= 0.75.1)
-  - FlipperKit/FlipperKitUserDefaultsPlugin (= 0.75.1)
-  - FlipperKit/SKIOSNetworkPlugin (= 0.75.1)
+  - Flipper-RSocket (~> 1.3)
+  - FlipperKit (~> 0.75.1)
+  - FlipperKit/Core (~> 0.75.1)
+  - FlipperKit/CppBridge (~> 0.75.1)
+  - FlipperKit/FBCxxFollyDynamicConvert (~> 0.75.1)
+  - FlipperKit/FBDefines (~> 0.75.1)
+  - FlipperKit/FKPortForwarding (~> 0.75.1)
+  - FlipperKit/FlipperKitHighlightOverlay (~> 0.75.1)
+  - FlipperKit/FlipperKitLayoutPlugin (~> 0.75.1)
+  - FlipperKit/FlipperKitLayoutTextSearchable (~> 0.75.1)
+  - FlipperKit/FlipperKitNetworkPlugin (~> 0.75.1)
+  - FlipperKit/FlipperKitReactPlugin (~> 0.75.1)
+  - FlipperKit/FlipperKitUserDefaultsPlugin (~> 0.75.1)
+  - FlipperKit/SKIOSNetworkPlugin (~> 0.75.1)
   - glog (from `../node_modules/react-native/third-party-podspecs/glog.podspec`)
   - RCT-Folly (from `../node_modules/react-native/third-party-podspecs/RCT-Folly.podspec`)
   - RCTRequired (from `../node_modules/react-native/Libraries/RCTRequired`)
@@ -712,6 +712,6 @@ SPEC CHECKSUMS:
   Yoga: 575c581c63e0d35c9a83f4b46d01d63abc1100ac
   YogaKit: f782866e155069a2cca2517aafea43200b01fd5a
 
-PODFILE CHECKSUM: 02b47f393048d297a31cee4132e6133d56992315
+PODFILE CHECKSUM: 9fe222ff44850b658732e6016d8198adb2fef518
 
 COCOAPODS: 1.10.1