Building the SDK will use cached protobuf definitions (if present) even in a clean checkout / build

## Expected Behavior

`git clone git@github.com:dapr/java-sdk.git && cd java-sdk && mvn package` should work out of the box, but it doesn't if you
have previously build the Java SDK with a different set of protobuf definitions. They instead get cached in `$HOME/.m2/repository/.cache/...` and the failure is non-obvious until you hunt around for docs on Maven's `wget` plugin.

## Actual Behavior

Build fails (iff the new code depends on protobuf definitions different than those you have in your cache).

## Steps to Reproduce the Problem

Have a set of protobuf files cached from a previous Java SDK build that differ from the ones required, then try building a clean clone -- it will fail.

## Release Note

RELEASE NOTE:

**FIX** Skip caching protobuf definition files to make `mvn clean` behave more as one would expect.