[proto] Remove redundant RPC GetLastCommittedBlockNumber() (hyperledger#155)

#### Type of change

- Improvement (improvement to code, performance, etc)

#### Description

- Remove redundant RPC in the coordinator:
`GetLastCommittedBlockNumber()` - It was already covered by
`GetNextExpectedBlockNumber()`
- Remove unnecessary stream check in `GetNextExpectedBlockNumber()` -
The sidecar verifies this anyway before calling this method
- Align API with VC - Replaced `GetLastCommittedBlockNumber()` with
`GetNextExpectedBlockNumber()`
- Adjust relevant tests

#### Related issues

- resolves hyperledger#48

Signed-off-by: Liran Funaro <liran.funaro@gmail.com>

Author: liran-funaro

api/protoblocktx/block_tx.pb.go

@@ -94,10 +94,6 @@ message BlockInfo {
     uint64 number = 1;
 }
 
-message LastCommittedBlock {
-    optional BlockInfo block = 1;
-}
-
 message QueryStatus {
     repeated string txIDs = 1;
 }

api/protoblocktx/block_tx.proto

@@ -16,8 +16,7 @@ import "google/protobuf/empty.proto";
 service Coordinator {
     rpc BlockProcessing(stream Batch) returns (stream protoblocktx.TransactionsStatus);
     rpc SetLastCommittedBlockNumber (protoblocktx.BlockInfo) returns (google.protobuf.Empty) {};
-    rpc GetLastCommittedBlockNumber (google.protobuf.Empty) returns (protoblocktx.LastCommittedBlock) {};
-    rpc GetNextExpectedBlockNumber (google.protobuf.Empty) returns (protoblocktx.BlockInfo) {};
+    rpc GetNextBlockNumberToCommit (google.protobuf.Empty) returns (protoblocktx.BlockInfo) {};
     rpc GetTransactionsStatus(protoblocktx.QueryStatus) returns (protoblocktx.TransactionsStatus);
     rpc GetConfigTransaction(google.protobuf.Empty) returns (protoblocktx.ConfigTransaction) {};
     rpc NumberOfWaitingTransactionsForStatus(google.protobuf.Empty) returns (WaitingTransactions);