It was only assigned to in `read_service_sheet`, and it's safe to remove
it also in `convert_service_sheet`.
Change-Id: Ia832cd8fea2d864e920907e455e834a3c3a724dd
We have some docs on how to install this, and we rely on the
requirements.txt file for specifying what packages are required. There's
no point in arbitrarily handling the `xlrd` package in a different
manner.
Change-Id: I2355440ada7fd0cc4868aeff5a8956729655c96b