tests: remove unnecessary igt_exit calls

Signed-off-by: Thomas Wood <thomas.wood@intel.com>

tests/gem_render_linear_blits.c

@@ -210,6 +210,4 @@ igt_main
 		intel_require_memory(count, SIZE, CHECK_RAM | CHECK_SWAP);
 		run_test(fd, count);
 	}
-
-	igt_exit();
 }

tests/gem_render_tiled_blits.c

@@ -223,6 +223,4 @@ igt_main
 		intel_require_memory(count, SIZE, CHECK_RAM | CHECK_SWAP);
 		run_test(fd, count);
 	}
-
-	igt_exit();
 }

tests/kms_3d.c

@@ -115,6 +115,4 @@ igt_simple_main
 
 	drmModeFreeConnector(connector);
 	free(edid);
-
-	igt_exit();
 }

tests/kms_force_connector.c

@@ -125,6 +125,4 @@ igt_main
 	igt_fixture {
 		drmModeFreeConnector(vga_connector);
 	}
-
-	igt_exit();
 }