Re-enable QueryCompilationTest.testAggregateJoinRemove

### Motivation
`pinot-query-planner/src/test/java/org/apache/pinot/query/QueryCompilationTest.java` still has `@Ignore` on `testAggregateJoinRemove()`. The ignore message says the test only passes when `PRUNE_RULES` run before `BASIC_RULES`, but enabling that changes roughly 50 hard-coded plans and may introduce redundant `Project` and `Exchange` nodes.

### Scope
- Reproduce the failing planner state.
- Decide whether the rule ordering, the expected plan, or the optimization itself is wrong.
- Re-enable the test once the intended behavior is explicit.

### Notes
Observed on `upstream/master` on April 15, 2026.

Start in pinot-query-planner/src/test/java/org/apache/pinot/query/QueryCompilationTest.java and reproduce the failure in testAggregateJoinRemove() on upstream/master. Inspect the PRUNE_RULES and BASIC_RULES ordering, the affected hard-coded plans, and any redundant Project or Exchange nodes. Done means the intended planner behavior is explicit and the test is re-enabled without unjustified plan changes.

Written by the indexing model from the issue text.