Remove run Metro hook from Xcode build, remove launchPackager scripts (#38242)

Summary:
Pull Request resolved: facebook/react-native#38242

See proposal: react-native-community/discussions-and-proposals#681

**Removed script files**

I searched GitHub (and specifically `react-native-windows/macos`) to confirm these files are not referenced:

- `scripts/launchPackager.bat`
- `scripts/launchPackager.command`
- `scripts/.packager.env`

Interestingly, React Native CLI refers to a `.packager.env` at a different location (`node_modules/.bin/`), and includes modified copies of `launchPackager.command/bat`. This PR removes duplication with these.

Changelog: [iOS][Breaking] Metro will no longer be started when running builds via Xcode

Reviewed By: cortinico

Differential Revision: D47297469

fbshipit-source-id: 06c3602d58b21ed693c3daa763d99947a70bfc5a

Original-Commit: facebook/react-native@dc68457

Author: huntie

template/ios/HelloWorld.xcodeproj/project.pbxproj

@@ -177,7 +177,6 @@
 			buildConfigurationList = 13B07F931A680F5B00A75B9A /* Build configuration list for PBXNativeTarget "HelloWorld" */;
 			buildPhases = (
 				C38B50BA6285516D6DCD4F65 /* [CP] Check Pods Manifest.lock */,
-				FD10A7F022414F080027D42C /* Start Packager */,
 				13B07F871A680F5B00A75B9A /* Sources */,
 				13B07F8C1A680F5B00A75B9A /* Frameworks */,
 				13B07F8E1A680F5B00A75B9A /* Resources */,
@@ -378,25 +377,6 @@
 			shellScript = "\"${PODS_ROOT}/Target Support Files/Pods-HelloWorld-HelloWorldTests/Pods-HelloWorld-HelloWorldTests-resources.sh\"\n";
 			showEnvVarsInLog = 0;
 		};
-		FD10A7F022414F080027D42C /* Start Packager */ = {
-			isa = PBXShellScriptBuildPhase;
-			buildActionMask = 2147483647;
-			files = (
-			);
-			inputFileListPaths = (
-			);
-			inputPaths = (
-			);
-			name = "Start Packager";
-			outputFileListPaths = (
-			);
-			outputPaths = (
-			);
-			runOnlyForDeploymentPostprocessing = 0;
-			shellPath = /bin/sh;
-			shellScript = "export RCT_METRO_PORT=\"${RCT_METRO_PORT:=8081}\"\necho \"export RCT_METRO_PORT=${RCT_METRO_PORT}\" > \"${SRCROOT}/../node_modules/react-native/scripts/.packager.env\"\nif [ -z \"${RCT_NO_LAUNCH_PACKAGER+xxx}\" ] ; then\n  if nc -w 5 -z localhost ${RCT_METRO_PORT} ; then\n    if ! curl -s \"http://localhost:${RCT_METRO_PORT}/status\" | grep -q \"packager-status:running\" ; then\n      echo \"Port ${RCT_METRO_PORT} already in use, packager is either not running or not running correctly\"\n      exit 2\n    fi\n  else\n    open \"$SRCROOT/../node_modules/react-native/scripts/launchPackager.command\" || echo \"Can't start packager automatically\"\n  fi\nfi\n";
-			showEnvVarsInLog = 0;
-		};
 /* End PBXShellScriptBuildPhase section */
 
 /* Begin PBXSourcesBuildPhase section */