Remove unused partial specialization for MatcherMethod<T>

No matcher actually uses it, and there is no good reason for it,
as the best it can do for user is removing a single indirection
when using the pointer inside the matcher. Given the overhead of
other code that will be running during such time, it is completely
meaningless.

This also fixes compilation for PredicateMatcher<const char*>.

projects/SelfTest/UsageTests/Matchers.tests.cpp

@@ -432,6 +432,10 @@ namespace { namespace MatchersTests {
             CHECK_THAT(actual, !UnorderedEquals(expected));
         }
 
+        TEST_CASE("Predicate matcher can accept const char*", "[matchers][compilation]") {
+            REQUIRE_THAT("foo", Predicate<const char*>([] (const char* const&) { return true; }));
+        }
+
 } } // namespace MatchersTests
 
 #endif // CATCH_CONFIG_DISABLE_MATCHERS