[Clang] Remove redundant -no-opaque-pointers flag in test (NFC)

This was accidentally caught in an automated replacement. This
test is testing the -opaque-pointers flag itself, so we shouldn't
add -no-opaque-pointers here (though it doesn't hurt either).

Also drop the line testing the default, as the default is now
determined by a cmake option.

clang/test/CodeGen/opaque-pointers-flag.c

 // NOTE: Assertions have been autogenerated by utils/update_cc_test_checks.py
-// RUN: %clang_cc1 -no-opaque-pointers -no-opaque-pointers -triple x86_64-unknown-unknown -emit-llvm %s -o - | FileCheck %s -check-prefix=TYPED
-// RUN: %clang_cc1 -no-opaque-pointers -opaque-pointers -triple x86_64-unknown-unknown -emit-llvm %s -o - | FileCheck %s -check-prefix=OPAQUE
-// The current default is typed pointers:
 // RUN: %clang_cc1 -no-opaque-pointers -triple x86_64-unknown-unknown -emit-llvm %s -o - | FileCheck %s -check-prefix=TYPED
+// RUN: %clang_cc1 -opaque-pointers -triple x86_64-unknown-unknown -emit-llvm %s -o - | FileCheck %s -check-prefix=OPAQUE
 
 // TYPED-LABEL: @test(
 // TYPED-NEXT:  entry: