Remove CODE_OF_CONDUCT.md and use the organization-wide CODE OF CONDUCT file (#8519)

Author: seisman

CODE_OF_CONDUCT.md

@@ -9,7 +9,7 @@
 [![Coverity](https://scan.coverity.com/projects/7153/badge.svg)](https://scan.coverity.com/projects/gmt)
 [![Documentation (development version)](https://img.shields.io/badge/docs-development-green.svg)](http://docs.generic-mapping-tools.org/dev/)
 [![GitHub release](https://img.shields.io/github/release/GenericMappingTools/gmt)](https://github.com/GenericMappingTools/gmt/releases)
-[![Contributor Covenant](https://img.shields.io/badge/Contributor%20Covenant-2.1-4baaaa.svg)](CODE_OF_CONDUCT.md)
+[![Contributor Covenant](https://img.shields.io/badge/Contributor%20Covenant-2.1-4baaaa.svg)](https://github.com/GenericMappingTools/.github/blob/main/CODE_OF_CONDUCT.md)
 [![DOI](https://zenodo.org/badge/DOI/10.5281/zenodo.3407865.svg)](https://zenodo.org/doi/10.5281/zenodo.3407865)
 
 ## What is GMT?