Remove CATCH_CONFIG_DISABLE_MATCHERS

Now that the recommended distribution and usage method is proper
library, users can just avoid including the matcher headers to get
basically the same effect.

tests/SelfTest/UsageTests/Matchers.tests.cpp

@@ -22,8 +22,6 @@
 
 namespace { namespace MatchersTests {
 
-#ifndef CATCH_CONFIG_DISABLE_MATCHERS
-
 #ifndef MATCHERS_TEST_HELPERS_INCLUDED // Don't compile this more than once per TU
 #define MATCHERS_TEST_HELPERS_INCLUDED
 
@@ -558,8 +556,6 @@ namespace { namespace MatchersTests {
 
 } } // namespace MatchersTests
 
-#endif // CATCH_CONFIG_DISABLE_MATCHERS
-
 #ifdef __clang__
 #pragma clang diagnostic pop
 #endif