gb: Remove comment about ABI changes from the Makefile

Okay. this comment thing has not worked (I totally forgot about it).
I think either we try to find ABI breakages with tools or we use
 #error macros and check for a version...
diff --git a/src/gb/Makefile.am b/src/gb/Makefile.am
index 076ad55..dd3f785 100644
--- a/src/gb/Makefile.am
+++ b/src/gb/Makefile.am
@@ -1,6 +1,3 @@
-# FIXME: LIBVERSION adjustments required for next version
-#  ABI of gprs_ns structure changed by adding DSCP.
-#
 # This is _NOT_ the library release version, it's an API version.
 # Please read Chapter 6 "Library interface versions" of the libtool documentation before making any modification
 LIBVERSION=3:0:0