With the resource-driven command-line configuration, we introduced the
option to ensure that only the PATH environment variable is edited only
minimally, i.e. only /cmd/ is added (as appropriate for _Git CMD_).
We are about to add another option, so let's refactor the equivalent of
Git's `strip_prefix()` function; It is not *quite* the same because we
have to `memmove()` the remainder to the beginning of the buffer.
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
0f4e555208