Followup to SERVER-61134. We realized the R primary doesn't need to know that R secondaries have finished copying files, it only needs to know they've done the subsequent step: importing files. (It can wait until then to kill its backup cursor, since D shouldn't be participating in backups or other migrations while it's donating to R.)

• Remove "copied files" state
• Remove "copied files" voting step (thus, there will be no steps)
• Change command name from voteCommitMigrationProgress to voteImportedFiles or something like that
• Merge the TenantMigrationRecipientCoordinator into the TenantMigrationRecipientService

Depends on SERVER-61144, which will call _advanceStableTimestampToStartApplyingDonorOpTime() earlier in the migration, which makes it safe for the primary to not wait for secondaries to copy files.