Revert "PLSR-1240 upgrade GRPC to 1.31 to avoid deadlock"

[lhotari]

Reverts #8351

• there are grpc/protobuf version compatibility issues and the master branch is currently broken

• tests weren't run when merging Upgrade GRPC to 1.31 to avoid deadlock #8351 because of [Github Flow] pom.xml change is considered a documentation change #8362

This reverts commit 647d3c2.

[lhotari]

There were this kind of errors in PR #8358 builds

13:11:31.285 [main] ERROR org.apache.bookkeeper.common.component.AbstractLifecycleComponent - Failed to start Component: storage-service
java.lang.NoSuchMethodError: io.grpc.internal.DnsNameResolverProvider.newNameResolver(Ljava/net/URI;Lio/grpc/Attributes;)Lio/grpc/internal/DnsNameResolver;
	at org.apache.bookkeeper.common.resolver.ServiceNameResolverProvider.newNameResolver(ServiceNameResolverProvider.java:95) ~[org.apache.bookkeeper-stream-storage-java-client-4.10.0.jar:4.10.0]
	at org.apache.bookkeeper.common.resolver.NameResolverProviderFactory.newNameResolver(NameResolverProviderFactory.java:45) ~[org.apache.bookkeeper-stream-storage-java-client-4.10.0.jar:4.10.0]
	at io.grpc.NameResolver$Factory.newNameResolver(NameResolver.java:207) ~[io.grpc-grpc-api-1.31.0.jar:1.31.0]
	at io.grpc.NameResolver$Factory.newNameResolver(NameResolver.java:235) ~[io.grpc-grpc-api-1.31.0.jar:1.31.0]
	at io.grpc.internal.ManagedChannelImpl.getNameResolver(ManagedChannelImpl.java:701) ~[io.grpc-grpc-core-1.31.0.jar:1.31.0]
	at io.grpc.internal.ManagedChannelImpl.<init>(ManagedChannelImpl.java:606) ~[io.grpc-grpc-core-1.31.0.jar:1.31.0]

in https://github.com/apache/pulsar/runs/1297863577?check_suite_focus=true

I was assuming that protoc-gen-grpc-java.version should match grpc.version. However this led to some other issues.
Therefore I think it's better to first revert the grpc upgrade, fix the Github flow (#8362) and then reissue a PR for the grpc upgrade. The PR #8361 could also be useful when doing the grpc upgrade PR.