Удаление патча

man patch 
...
       -R  or  --reverse
          Assume that this patch was  created  with  the  old  and  new  files
          swapped.   (Yes,  I'm  afraid  that  does happen occasionally, human
          nature being what it is.)  patch attempts to swap each  hunk  around
          before applying it.  Rejects come out in the swapped format.  The -R
          option does not work with ed diff scripts because there is too  lit‐
          tle information to reconstruct the reverse operation.

          If  the  first hunk of a patch fails, patch reverses the hunk to see
          if it can be applied that way.  If it can, you are asked if you want
          to  have  the -R option set.  If it can't, the patch continues to be
          applied normally.  (Note: this method cannot detect a reversed patch
          if  it  is a normal diff and if the first command is an append (i.e.
          it should have been a delete) since appends always succeed,  due  to
          the  fact  that  a  null  context  matches  anywhere.  Luckily, most
          patches add or  change  lines  rather  than  delete  them,  so  most
          reversed  normal  diffs begin with a delete, which fails, triggering
          the heuristic.)
...

Apply patch:

patch -p1 < ../patch-x.y.z

Undo patch:

patch -R -p1 < ../patch-x.y.z