[streambuf.general] Remove incorrect "abstract"

PJBoy · web-flow · commit 82b2ba6f6245 · 2023-11-08T02:10:58.000Z
The referenced class template `basic_streambuf` is not abstract.
diff --git a/source/iostreams.tex b/source/iostreams.tex
@@ -3096,7 +3096,7 @@
 \pnum
 The class template
 \tcode{basic_streambuf}
-serves as an abstract base class for deriving various
+serves as a base class for deriving various
 \term{stream buffers}
 whose objects each control two
 \term{character sequences}:
