Dual Y axis lines in grid section of Chart

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## What did you do?

Provided data to chart for drawing the graph

## What did you expect to happen?

Unique lines of set of two data.

## What happened instead?

Redundant lines in Y axis.

## Charts Environment

**Charts version/Branch/Commit Number:
**Xcode version:**
**Swift version:**
**Platform(s) running Charts:**
**macOS version running Xcode:**

## Demo Project

Start by reproducing the reported dual-Y-axis chart behavior in the Charts repository using the attached screenshot and the issue's data description. Trace the grid and Y-axis rendering entry points, then verify that the chart displays unique lines for the two data sets without redundant Y-axis lines.

Written by the indexing model from the issue text.