Remove force GOVUK_PROMETHEUS_EXPORTER

GovukPrometheusExporter is now always initialised. See [PR 361 on govuk_app_config](alphagov/govuk_app_config#361)

Author: stringiest

config/environments/development.rb

@@ -44,6 +44,3 @@
   # Apply autocorrection by RuboCop to files generated by `bin/rails generate`.
   config.generators.apply_rubocop_autocorrect_after_generate!
 end
-
-# TODO: remove this workaround once GovukPrometheusExporter initialisation is fixed in govuk_app_config.
-ENV["GOVUK_PROMETHEUS_EXPORTER"] = "force"

config/environments/test.rb

@@ -46,6 +46,3 @@
   config.discovery_engine_default_collection_name = "[collection]"
   config.discovery_engine_default_location_name = "[location]"
 end
-
-# TODO: remove this workaround once GovukPrometheusExporter initialisation is fixed in govuk_app_config.
-ENV["GOVUK_PROMETHEUS_EXPORTER"] = "force"