binman: Clean up unnecessary code related to ELF test files

We use the Makefile for all ELF test files now, so drop all the code that
checks whether to get the test file from the Makefile or from the git
repo.

Also add a comment to the Makefile indicating that it is run from binman.

Signed-off-by: Simon Glass <sjg@chromium.org>

tools/binman/elf_test.py

@@ -69,10 +69,7 @@ def BuildElfTestFiles(target_dir):
     if 'MAKEFLAGS' in os.environ:
         del os.environ['MAKEFLAGS']
     tools.Run('make', '-C', target_dir, '-f',
-              os.path.join(testdir, 'Makefile'), 'SRC=%s/' % testdir,
-              'bss_data', 'u_boot_ucode_ptr', 'u_boot_no_ucode_ptr',
-              'u_boot_binman_syms', 'u_boot_binman_syms.bin',
-              'u_boot_binman_syms_size', 'u_boot_binman_syms_bad')
+              os.path.join(testdir, 'Makefile'), 'SRC=%s/' % testdir)
 
 
 class TestElf(unittest.TestCase):