HOTFIX: Removes the command 'flutter clean' on building for iOS

The command got an update a earlier this year. It now deletes the file `Generated.xcconfig` which is needed by Xcode during archive.

tools/build.triggerBuild.sh

@@ -99,7 +99,6 @@ function iosReleaseBuild {
     echo "iOS release build for ${flavor} started"
     rm -rf ../ios/Flutter/Flutter.framework
     flutter build ios --release --build-name=${buildName} --build-number=${buildNumber} --flavor ${flavor}
-    flutter clean
 
     xcodebuild -workspace ios/Runner.xcworkspace -scheme ${flavor} -sdk iphoneos -configuration Release-${flavor} archive -archivePath "${IOS_BUILD_FOLDER}/Runner.xcarchive" -allowProvisioningUpdates | xcpretty
     xcodebuild -exportArchive -archivePath "${IOS_BUILD_FOLDER}/Runner.xcarchive" -exportOptionsPlist ios/exportOptions${flavor}.plist -exportPath "${IOS_BUILD_FOLDER}/Runner.ipa" -allowProvisioningUpdates | xcpretty