Remove package merge-graphql-schemas and substitute with simple string concatonation

[asishallab]

The schema of our GraphQL application is spread over several independent modules. Each of these defines its part of the schema as a string which then is exported. These strings need to be concatonated into a single string which then is provided to GraphQL as the schema.

There is no need to use the package 'merge-graphql-schemas'. Remove it and use string concatonation.