Revert "PrintAsObjc Test: Test compatibility headers for C"

This reverts commit d5b3132.

Author: hamishknight

test/PrintAsObjC/cdecl-imports.swift

@@ -2,7 +2,6 @@
 // RUN: %target-swift-frontend(mock-sdk: %clang-importer-sdk) %s -parse-as-library -typecheck -verify -emit-objc-header-path %t/swift.h
 // RUN: %FileCheck %s < %t/swift.h
 // RUN: %check-in-clang %t/swift.h
-// RUN: %check-in-clang-c %t/swift.h
 // RUN: %check-in-clang-cxx %t/swift.h
 
 // REQUIRES: objc_interop

test/PrintAsObjC/cdecl.swift

@@ -4,7 +4,6 @@
 // RUN: %FileCheck %s < %t/cdecl.h
 // RUN: %check-in-clang %t/cdecl.h
 // RUN: %check-in-clang -fno-modules -Qunused-arguments %t/cdecl.h -include ctypes.h -include CoreFoundation.h
-// RUN: %check-in-clang-c -fno-modules -Qunused-arguments %t/cdecl.h -include ctypes.h -include CoreFoundation.h
 // RUN: %check-in-clang-cxx -fno-modules -Qunused-arguments %t/cdecl.h -include ctypes.h -include CoreFoundation.h
 
 // REQUIRES: objc_interop

test/PrintAsObjC/lit.local.cfg

@@ -10,15 +10,6 @@ config.substitutions.insert(0, ('%check-in-clang',
   '-I %%clang-include-dir '
   '-isysroot %r/Inputs/clang-importer-sdk' % config.test_source_root) )
 
-config.substitutions.insert(0, ('%check-in-clang-c',
-  '%%clang -fsyntax-only -x c-header -std=c99 -fobjc-arc -fmodules '
-  '-fmodules-validate-system-headers '
-  '-Weverything -Werror -Wno-unused-macros -Wno-incomplete-module '
-  '-Wno-auto-import '
-  '-F %%clang-importer-sdk-path/frameworks '
-  '-I %%clang-include-dir '
-  '-isysroot %r/Inputs/clang-importer-sdk' % config.test_source_root) )
-
 config.substitutions.insert(0, ('%check-in-clang-cxx',
   '%%clang -fsyntax-only -x objective-c++-header -std=c++17 '
   '-fobjc-arc -fmodules -fmodules-validate-system-headers '