[basic.scope.scope] Replaced the term top-level reference with just reference

[basic.scope.scope] Replaced the term top-level reference with just reference in light of [this issue](cplusplus/CWG#569)

Author: ranaanoop

source/basic.tex

@@ -917,7 +917,7 @@
 exactly one is an implicit object member function
 with no \grammarterm{ref-qualifier} and
 the types of their object parameters\iref{dcl.fct},
-after removing top-level references,
+after removing references,
 are the same, or
 \item
 their object parameters have the same type.