charter: remove meeting attendance requirement

This commit removes the requirement for TSC meeting
attendance. After this change, there is currently only one
item in the list of TSC member requirements. I decided to
leave the list in place under the assumption that other
list items may be added in the future.

Fixes: #1338

TSC-Charter.md

@@ -65,7 +65,6 @@ TSC members are expected to regularly participate in TSC activities.
 A TSC member is automatically removed from the TSC if, during a 3-month period,
 all of the following are true:
 
-* They attend fewer than 25% of the regularly scheduled meetings.
 * They do not participate in any TSC votes.
 
 ## Section 4. Responsibilities of the TSC