Reflect new attachment limit

[Klaas-]

redhat-support-lib-python/src/redhat_support_lib/utils/confighelper.py

Line 65 in bf2d9a5

self.attachment_max_size = 1 * 1024 * 1024 * 1024 # 1GB

should reflect the new limit of 250GB and in general dropbox.redhat.com support should be dropped according to welcome message on that ftp:

220-+---------------------------------------------------------------+
220-|        Welcome to Red Hat Global Support Services FTP!        |
220-|                                                               |
220-|      Now you can upload files up to 250GB in size directly    |
220-|   to the Customer Portal. With this new capability, you can   |
220-|     manage everything in one place. You can start taking      |
220-|        advantage of this improved functionality now.          |
220-|                                                               |
220-|    Access to dropbox.redhat.com and dropbox-ssl.redhat.com    |
220-|   will no longer be available on March 1, 2019. Please visit  |
220-|     https://access.redhat.com/solutions/2112 for details.     |
220-+---------------------------------------------------------------+

Greetings
Klaas