buildman: Drop -I option

This has been deprecated with a notice that it will be removed after April
2021. Drop it now.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/buildman/cmdline.py b/tools/buildman/cmdline.py
index 8586bdf..ddcb1ec 100644
--- a/tools/buildman/cmdline.py
+++ b/tools/buildman/cmdline.py
@@ -59,9 +59,6 @@
     parser.add_option('-i', '--in-tree', dest='in_tree',
           action='store_true', default=False,
           help='Build in the source tree instead of a separate directory')
-    # -I will be removed after April 2021
-    parser.add_option('-I', '--incremental', action='store_true',
-          default=False, help='Deprecated, does nothing. See -m')
     parser.add_option('-j', '--jobs', dest='jobs', type='int',
           default=None, help='Number of jobs to run at once (passed to make)')
     parser.add_option('-k', '--keep-outputs', action='store_true',
diff --git a/tools/buildman/control.py b/tools/buildman/control.py
index 8f4810b..beade62 100644
--- a/tools/buildman/control.py
+++ b/tools/buildman/control.py
@@ -176,9 +176,6 @@
         print()
         return 0
 
-    if options.incremental:
-        print(col.build(col.RED,
-                        'Warning: -I has been removed. See documentation'))
     if not options.output_dir:
         if options.work_in_output:
             sys.exit(col.build(col.RED, '-w requires that you specify -o'))