'New metric' button should not be duplicated on custom metrics page

Summary

There are two 'new metrics' buttons on the default state of the custom metrics field, this is not desired

Steps to reproduce

Grab any project with an active prometheus integration and go to

Settings -> Integrations -> Prometheus

What is the current bug behavior?

• There are two 'new metrics' buttons
• Font of 'new metrics' is much larger than it should be

What is the expected correct behavior?

• There is 1 'new metrics' button
• Font size of 'new metrics' and 'custom metrics' is the same