Remove node_stack Peek templating where possible (#4801)

The "templated for consistency" variants felt a little confusing when I
was working on #4795, so suggesting to remove templating where it's not
helpful to instantiate (particularly when there were both templated and
non-templated variants). Note this leaves a `PeekIs<IdT>` because
there's indirection there, but that's more the exception than the rule.

toolchain/check/handle_binding_pattern.cpp

@@ -77,7 +77,7 @@ static auto HandleAnyBindingPattern(Context& context, Parse::NodeId node_id,
 
   // A `self` binding can only appear in an implicit parameter list.
   if (name_id == SemIR::NameId::SelfValue &&
-      !context.node_stack().PeekIs<Parse::NodeKind::ImplicitParamListStart>()) {
+      !context.node_stack().PeekIs(Parse::NodeKind::ImplicitParamListStart)) {
     CARBON_DIAGNOSTIC(
         SelfOutsideImplicitParamList, Error,
         "`self` can only be declared in an implicit parameter list");