update message part content on "Trial mode" page

[dmvancura]

Who discovered this?

deana

What happened?

content should no longer say "parts" when referring to messages

Environment

production

What pages did this appear on?

Trial mode page, 5 spots

Detail the steps for someone to reproduce

update multiple lines on this page to remove the word "parts" but ensure the statements and accurate and useful

first bullet point under Limits while in trial mode, update to "parts" to "messages"

second fill sentence under Limits while in trial mode, change "parts" to "messages"

third bullet point under Limits while in trial mode, update to Generally, 160 characters is one text message.
fourth bullet point under Limits while in trial mode, update to And 160-306 characters count as two text messages.

remove last sentence under Limits while in trial mode "For more information on how message parts are calculated, see Tracking usage."

What browsers are you seeing the problem on?

Chrome

Relevant log output