[allocator.requirements.general] Remove redundant template syntax

In the Cpp17Allocator requirements, all identifiers name specific
types, not type-dependent code in a template, even if they are
template instantiations.  Hence, all use of `::template` is redundant.
Not in the sense of we are awaiting LWG to review P2150 for policy,
but in the sense these have been redundant since C++11, and were
outright ill-formed prior to that.

Author: AlisdairM

source/lib-intro.tex

@@ -2234,7 +2234,7 @@
 \end{itemdescr}
 
 \begin{itemdecl}
-typename X::template rebind<U>::other
+typename X::rebind<U>::other
 \end{itemdecl}
 
 \begin{itemdescr}