[clang][test] Make check pattern shorter

A check pattern in clang/test/SemaCXX/template-64605.cpp contains template
specialization kind (the text "implicit_instantiation"). It does not need to
be checked and can be safely removed.

Presence of this text in the check pattern prevents from backporting some
commits to the release branch: #64605.
It has only recently been printed and the relevant commit is not present in
the release/17.x branch.

Author: spavloff

clang/test/SemaCXX/template-64605.cpp

@@ -16,7 +16,7 @@ int f() { return b_64605<void>(); }
 // CHECK:      ImplicitCastExpr {{.*}} 'float' <IntegralToFloating> RoundingMath=1 AllowFEnvAccess=1
 // CHECK-NEXT: IntegerLiteral {{.*}} 4294967295
 
-// CHECK:      FunctionDecl {{.*}} b_64605 'int ()' implicit_instantiation
+// CHECK:      FunctionDecl {{.*}} b_64605 'int ()'
 // CHECK-NEXT: TemplateArgument type 'void'
 
 // CHECK:      ImplicitCastExpr {{.*}} 'float' <IntegralToFloating> RoundingMath=1 AllowFEnvAccess=1