Remove docker images for pgr v2.6.1, 2.6.2, 2.6.3

[krashish8]

Fixes #50

Changes proposed in this pull request:

• Deleted the pgRouting docker images folders:
  • 10-2.5-2.6.1
  • 10-2.5-2.6.2
  • 10-2.5-2.6.3
  • 11-2.5-2.6.1
  • 11-2.5-2.6.2
  • 11-2.5-2.6.3
  • 12-3.0-2.6.3

Please look at @sanak's comment before merging this: https://github.com/pgRouting/docker-pgrouting/issues/50#issuecomment-1170756633

@pgRouting/admins

[sanak]

@krashish8 I missed the README.md pgRouting v2 part. Those part can be deleted or updated.

• https://github.com/pgRouting/docker-pgrouting/blob/remove-unsupported-images/README.md?plain=1#L46-L53
• https://github.com/pgRouting/docker-pgrouting/blob/remove-unsupported-images/README.md?plain=1#L67-L90

[krashish8]

Thanks, done!