Remove proxy table

[anupama-pathirage]

Purpose

The proxy table was mainly added to support streaming table join use cases. But now we have decided to follow the approach given under proposal #1 (refer doc [1]) which does not requires proxy tables.

[1] https://docs.google.com/document/d/1ubwKtIG3tzRiwIilzvgo-DMel4Ex8UmHiYc3NxCXrqM/edit#

Also update/remove from proxy table based on a condition is in-efficient as the condition has to evaluate after selecting data , iterate full data set, find the matching results and then again we have to send delete or update query to the DB. So no practical usage for the proxy table and everything can be achieved using jdbc connector.

With this PR below issue also can be closed.
#6998

BBE changes:
ballerina-attic/ballerina-examples#1061

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