[#22339] YSQL: Remove query plan costs from yb_planner_joins regressi…

…on tests

Summary:
These tests do not need costs in explain's output
Jira: DB-11244

Test Plan: ./yb_build.sh --java-test 'org.yb.pgsql.TestPgRegressPlanner'

Reviewers: gkukreja, jason, tnayak

Reviewed By: jason

Subscribers: yql

Tags: #jenkins-ready

Differential Revision: https://phorge.dev.yugabyte.com/D34929