[chore] Remove migration for managing sdk/go/**/schema.go in .gitignore

[pgavlin]

#1992 added a migration to ensure that bridged providers aren't unintentionally excluding sdk/go/**/schema.go. This tracks removing the migration once it has been rolled out to all affected providers.

Affected providers:

• pulumi/pulumi-alicloud
• pulumi/pulumi-azure
• pulumi/pulumi-azuread
• pulumi/pulumi-azuredevops
• pulumi/pulumi-confluent
• pulumi/pulumi-consul
• pulumi/pulumi-dnsimple
• pulumi/pulumi-docker
• pulumi/pulumi-equinix-metal
• pulumi/pulumi-fastly
• pulumi/pulumi-gcp
• pulumi/pulumi-github
• pulumi/pulumi-gitlab
• pulumi/pulumi-hcloud
• pulumi/pulumi-kafka
• pulumi/pulumi-kong
• pulumi/pulumi-mailgun
• pulumi/pulumi-mysql
• pulumi/pulumi-newrelic
• pulumi/pulumi-ns1
• pulumi/pulumi-rabbitmq
• pulumi/pulumi-random
• pulumi/pulumi-rke
• pulumi/pulumi-snowflake
• pulumi/pulumi-spotinst
• pulumi/pulumi-terraform
• pulumi/pulumi-tls
• pulumi/pulumi-vsphere
• pulumi/pulumi-wavefront
• pulumi/pulumi-xyz
• pulumi/pulumi-yandex