Remove nullability specifiers

src/objective-c/GRPCClient/private/GRPCHost.h

@@ -54,7 +54,7 @@ struct grpc_channel_credentials;
 
 /** Create a grpc_call object to the provided path on this host. */
 - (nullable struct grpc_call *)unmanagedCallWithPath:(NSString *)path
-                                          serverName:(nullable NSString *)serverName
+                                          serverName:(NSString *)serverName
                                      completionQueue:(GRPCCompletionQueue *)queue;
 
 // TODO: There's a race when a new RPC is coming through just as an existing one is getting

src/objective-c/GRPCClient/private/GRPCHost.m

@@ -120,7 +120,7 @@ static GRPCConnectivityMonitor *connectivityMonitor = nil;
 }
 
 - (nullable grpc_call *)unmanagedCallWithPath:(NSString *)path
-                                   serverName:(nullable NSString *)serverName
+                                   serverName:(NSString *)serverName
                               completionQueue:(GRPCCompletionQueue *)queue {
   GRPCChannel *channel;
   // This is racing -[GRPCHost disconnect].

src/objective-c/GRPCClient/private/GRPCWrappedCall.h

@@ -75,7 +75,7 @@
 @interface GRPCWrappedCall : NSObject
 
 - (instancetype)initWithHost:(NSString *)host
-                  serverName:(nullable NSString *)serverName
+                  serverName:(NSString *)serverName
                         path:(NSString *)path NS_DESIGNATED_INITIALIZER;
 
 - (void)startBatchWithOperations:(NSArray *)ops errorHandler:(void(^)())errorHandler;

src/objective-c/GRPCClient/private/GRPCWrappedCall.m

@@ -236,7 +236,7 @@
 }
 
 - (instancetype)initWithHost:(NSString *)host
-                  serverName:(nullable NSString *)serverName
+                  serverName:(NSString *)serverName
                         path:(NSString *)path {
   if (!path || !host) {
     [NSException raise:NSInvalidArgumentException