Fix broken build when DEBUG_GLYPHS is set

Some of the logging lines referred to the "path" variable which no
longer exists. We log the Harfbuzz script instead, which hopefully
provides enough context.

This change only affects debug builds, but we will want to be working
intensively in this space.

Change-Id: I86c3b58c9fa2a8c47812ef5f0b5ce64fd8dcdc20