Shippable: fix bin/java-petstore-webclient.sh

Created by: jmini

PR checklist

• Read the contribution guidelines.
• Ran the shell script under ./bin/ to update Petstore sample so that CIs can verify the change. (For instance, only need to run ./bin/{LANG}-petstore.sh and ./bin/security/{LANG}-petstore.sh if updating the {LANG} (e.g. php, ruby, python, etc) code generator or {LANG} client's mustache templates). Windows batch files can be found in .\bin\windows\.
• Filed the PR against the correct branch: master, 3.1.x, 4.0.x. Default: master.
• Copied the technical committee to review the pull request if your PR is targeting a particular programming language.

Description of the PR

The script bin/java-petstore-webclient.sh introduced with #435 by @0v1se produces this output:

...
./bin/run-all-petstore
...
Running ./bin/java-petstore-webclient.sh
# START SCRIPT: ./bin/java-petstore-webclient.sh
Removing files and folders under samples/client/petstore/java/webclient/src/main
Java HotSpot(TM) 64-Bit Server VM warning: ignoring option MaxPermSize=256M; support was removed in 8.0
[main] INFO  o.o.c.ignore.CodegenIgnoreProcessor - No .openapi-generator-ignore file found.
...
cp: cannot stat 'CI/samples.ci/client/petstore/java/test-manual/webclient/ApiClientTest.java': No such file or directory
cp: cannot stat 'CI/samples.ci/client/petstore/java/test-manual/webclient/auth/ApiKeyAuthTest.java': No such file or directory
cp: cannot stat 'CI/samples.ci/client/petstore/java/test-manual/webclient/auth/HttpBasicAuthTest.java': No such file or directory
cp: cannot stat 'CI/samples.ci/client/petstore/java/test-manual/webclient/model/EnumValueTest.java': No such file or directory
ERROR!! FAILED TO RUN ./bin/java-petstore-webclient.sh
...
[ERROR] 1 out of 184 scripts failed.

The fix consist of removing the copy file section. It seems that there is no manually written unit test at the indicated location.