Fix `removeGlobalContexts` not removing expected context

[paulboocock]

Describe the bug
When calling removeGlobalContexts the equality statement is backwards, so it removes unexpected schemas.

snowplow-javascript-tracker/libraries/tracker-core/src/contexts.ts

Line 199 in c2e3ccb

globalPrimitives = globalPrimitives.filter((item) => JSON.stringify(item) === JSON.stringify(context));

To Reproduce

    window.snowplow('addGlobalContexts', [{
      schema: 'iglu:com.snowplowanalytics.snowplow/schema1/jsonschema/1-0-0',
      data: {
        prop1: 'hello'
      }
    },
    {
      schema: 'iglu:com.snowplowanalytics.snowplow/schema2/jsonschema/1-0-0',
      data: {
        prop2: 'hello2'
      }
    }]);
    window.snowplow('trackPageView');
    window.snowplow('removeGlobalContexts', [{
      schema: 'iglu:com.snowplowanalytics.snowplow/schema2/jsonschema/1-0-0',
      data: {
        prop2: 'hello2'
      }
    }]);
    window.snowplow('trackPageView');

Expected behavior
With this, schema1 is removed, when it is expected that schema2 should be removed.