Build: Remove .PRECIOUS flags.

Build: Remove .PRECIOUS flags.

Since 820c7ff5d380e8ca52057717ab3176b5e40107fd all files are treated as
.SECONDARY files. This means that `make' will not delete files that it
identifies as intermediate files, which would be it's default behavior
otherwise.

Currently, lexer and parser files, some font files, and some postscript
files are treated as .PRECIOUS in the build. This means that `make'
will never delete these files, even when the rule for creating them
failed. It seems that these files were flagged as .PRECIOUS in order
to keep them around after a successful build, preventing `make' from
removing them. But treating these files as .SECONDARY is sufficient
for this purpose. The .PRECIOUS flag introduces potential problems
that we would rather avoid.