efi_selftest: remove redundant function efi_st_memcmp()

Function memcmp() is available in efi_freestanding.c. So we do not remove a
further implementation.

Replace all usages of efi_st_memcmp() by memcmp().

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
diff --git a/lib/efi_selftest/efi_selftest_startimage_exit.c b/lib/efi_selftest/efi_selftest_startimage_exit.c
index 96049de..11207b8 100644
--- a/lib/efi_selftest/efi_selftest_startimage_exit.c
+++ b/lib/efi_selftest/efi_selftest_startimage_exit.c
@@ -139,7 +139,7 @@
 		return EFI_ST_FAILURE;
 	}
 	if (!exit_data || exit_data_size != sizeof(expected_text) ||
-	    efi_st_memcmp(exit_data, expected_text, sizeof(expected_text))) {
+	    memcmp(exit_data, expected_text, sizeof(expected_text))) {
 		efi_st_error("Incorrect exit data\n");
 		return EFI_ST_FAILURE;
 	}