pmbootstrap -s: remove option (!1868)

Remove in favor of similar, but more visible "--no-install" option for
"pmbootstrap flasher" and "pmbootstrap export".

It seems that the option wasn't really used by anybody, so let's just
remove it without a deprication period. If dear reader thinks otherwise
after this is merged, and is not happy with "--no-install", please state
your reasoning in a new issue, so we can discuss it.

Related: !1863

pmb/parse/arguments.py

@@ -311,9 +311,6 @@ def arguments():
     parser.add_argument("-j", "--jobs", help="parallel jobs when compiling")
     parser.add_argument("-p", "--aports",
                         help="postmarketos aports (pmaports) path")
-    parser.add_argument("-s", "--skip-initfs", dest="skip_initfs",
-                        help="do not re-generate the initramfs",
-                        action="store_true")
     parser.add_argument("-t", "--timeout", help="seconds after which processes"
                         " get killed that stopped writing any output (default:"
                         " 900)", default=900, type=float)