README.md: Remove 'multi-slot ul tbf' line from 'Current Limitations'

This feature was implemented in commit
ed2afa3bed4c1b7a2bffae6be7df881de4f976e7, ~3 years ago.

Change-Id: I9abe54f280ab4e62c0c5220d010575b912c8c141
diff --git a/README.md b/README.md
index 3d11a78..8467c50 100644
--- a/README.md
+++ b/README.md
@@ -78,7 +78,6 @@
  * No fixed allocation support (was removed from 3GPP Rel >= 5 anyway)
  * No extended dynamic allocation support
  * No unacknowledged mode operation
- * Only single slot assignment on uplink direction
  * No half-duplex class support (only semi-duplex)
  * No TA loop
  * No power loop