This script looks for existing definitions with the `SPIRV_` prefix, so
that it can preserve them when updating the file. When the commit
2d62833048 changed the prefix from `SPV_`,
the number of characters to strip from matched names was not updated,
which broke this feature. This commit fixes remaining cases that weren't
fixed by 339c87a8a0.
The relationship of this script to the files it is meant to maintain is
still bitrotten in other ways.
bc6834f5c7