freetype: don't expose harfbuzz directly from freetype pkg

This declaration itself was nonsensical, as the file being imported was
from the harfbuzz package (instead users should import harfbuzz
directly). But as well as being nonsensical, this line was occasionally
triggering a stage2 bug which we haven't quite tracked down yet which
seems to be something to do with conflicting modules importing a file.
This issue meant that projects with a specific dependency pattern on
freetype and harfbuzz would sometimes randomly get a nonsensical
compilation error. This change works around that issue for
mach-freetype.

libs/freetype/src/main.zig

@@ -7,7 +7,6 @@ pub usingnamespace @import("stroke.zig");
 pub usingnamespace @import("types.zig");
 pub usingnamespace @import("computations.zig");
 pub usingnamespace @import("error.zig");
-pub const harfbuzz = @import("harfbuzz/main.zig");
 pub const c = @import("c.zig");
 
 const std = @import("std");