NCGenerics: adjust number of diagnostics

Something I changed in the implementation of NoncopyableGenerics has
gotten the number back down to 6, where it was before I started :)

Author: kavon

validation-test/compiler_crashers_2_fixed/0161-issue-49119.swift

@@ -8,8 +8,8 @@ protocol P {
 
 struct Type<Param> {}
 extension Type: P where Param: P, Param.A == Type<Param> {
-  // expected-error@-1 7{{extension of generic struct 'Type' has self-referential generic requirements}}
-  // expected-note@-2 7{{through reference here}}
+  // expected-error@-1 6{{extension of generic struct 'Type' has self-referential generic requirements}}
+  // expected-note@-2 6{{through reference here}}
   // expected-error@-3 {{type 'Type<Param>' does not conform to protocol 'P'}}
   typealias A = Param
   // expected-note@-1 2{{through reference here}}