Examples: remove references to catch_default_main

catch_default_main.hpp was removed in db32550898

The example 000-CatchMain.cpp is no longer compiled, but is still
present in the examples and is still references by other example
files. Remove the file and references to it, as they are confusing.

examples/120-Bdd-ScenarioGivenWhenThen.cpp

@@ -1,6 +1,6 @@
 // 120-Bdd-ScenarioGivenWhenThen.cpp
 
-// main() provided in 000-CatchMain.cpp
+// main() provided by linkage with Catch2WithMain
 
 #include <catch2/catch_test_macros.hpp>
 
@@ -48,8 +48,8 @@ SCENARIO( "vectors can be sized and resized", "[vector]" ) {
 }
 
 // Compile & run:
-// - g++ -std=c++11 -Wall -I$(CATCH_SINGLE_INCLUDE) -o 120-Bdd-ScenarioGivenWhenThen 120-Bdd-ScenarioGivenWhenThen.cpp 000-CatchMain.o && 120-Bdd-ScenarioGivenWhenThen --success
-// - cl -EHsc -I%CATCH_SINGLE_INCLUDE% 120-Bdd-ScenarioGivenWhenThen.cpp 000-CatchMain.obj && 120-Bdd-ScenarioGivenWhenThen --success
+// - g++ -std=c++11 -Wall -I$(CATCH_SINGLE_INCLUDE) -o 120-Bdd-ScenarioGivenWhenThen 120-Bdd-ScenarioGivenWhenThen.cpp && 120-Bdd-ScenarioGivenWhenThen --success
+// - cl -EHsc -I%CATCH_SINGLE_INCLUDE% 120-Bdd-ScenarioGivenWhenThen.cpp && 120-Bdd-ScenarioGivenWhenThen --success
 
 // Expected compact output (all assertions):
 //