To remove the patch patch-2.4.28.tar.bz2 from a kernel source tree, the command that must be used is:

How do I apply or revert a patch?
the option -Rp1 must mean Revert patch

—
You apply a patch with the `patch’ program. The patch program reads a diff
(or patch) file and makes the changes to the source tree described in it.

Patches for the Linux kernel are generated relative to the parent directory
holding the kernel source dir.

This means that paths to files inside the patch file contain the name of the
kernel source directories it was generated against (or some other directory
names like “a/” and “b/”).
Since this is unlikely to match the name of the kernel source dir on your
local machine (but is often useful info to see what version an otherwise
unlabeled patch was generated against) you should change into your kernel
source directory and then strip the first element of the path from filenames
in the patch file when applying it (the -p1 argument to `patch’ does this).

To revert a previously applied patch, use the -R argument to patch.
So, if you applied a patch like this:
patch -p1 < ../patch-x.y.z

You can revert (undo) it like this:
patch -R -p1 < ../patch-x.y.z

https://www.kernel.org/doc/Documentation/applying-patches.txt