Revert "Enable bitcode for ios native libraries" in v1.24.x

[jtattermusch]

Reverts #20113 in the release branch.
The size increase of the libgrpc.a is way too much to be shipped as part of Grpc.Core nuget (right now libgrpc.a is >250MB).

FYI @koshelevpavel if we don't figure out a good way how to decrease the size or iOS binaries, we'll need to revert.

[veblush]

LGTM.

[veblush]

For a long term solution, can we split single big nuget package into several pieces? If nuget supports a way having multiple files depending on each platform like python, it'd be great. Otherwise, we might able to split a nuget package into several using dependency?

For example,

• gRPC.Core package
  • Dependency (netstandard2.0) -> gRPC.Core.NetStandard2 package
  • Dependency (xamarinios) -> gRPC.Core.Xamarin.iOS package
  • ...

From the apple doc, bitcode is not mandatory for iOS but it is for watchOS and tvOS. I'm not sure how many watchOS and tvOS apps are written in .NET & gRPC but probably we will have to solve this problem in future.

[jtattermusch]

@veblush yes, we want to split the Grpc.Core package, but the exact way of achieving that is not clear (and it's not really well documented by microsoft). We actually want to split packages by runtimes (linux, win, mac, ....) rather than by target frameworks, because it's the native libraries that are big.