Remove build systems other than CMake

Make it clear that CMake is the only supported build system.

Signed-off-by: Kevin Petit <kevin.petit@arm.com>

test_conformance/subgroups/Jamfile

@@ -1,26 +0,0 @@
-project
-    : requirements
-      <toolset>gcc:<cflags>-xc++
-      <toolset>msvc:<cflags>"/TP"
-    ;
-exe test_subgroups
-    : main.cpp
-      test_queries.cpp
-      test_workitem.cpp
-      test_workgroup.cpp
-      test_barrier.cpp
-      ../../test_common/harness/errorHelpers.c
-      ../../test_common/harness/threadTesting.c
-      ../../test_common/harness/testHarness.c
-      ../../test_common/harness/mt19937.c
-      ../../test_common/harness/conversions.c
-      ../../test_common/harness/kernelHelpers.c
-      ../../test_common/harness/mt19937.c
-    : <target-os>windows:<source>../../test_common/harness/msvc9.c
-    ;
-install dist
-    : test_subgroups
-    : <variant>debug:<location>$(DIST)/debug/tests/test_conformance/subgroups
-      <variant>release:<location>$(DIST)/release/tests/test_conformance/subgroups
-    ;
-