Restore host building on request from a user. Apparently, packages
outside of openwrt/packages feed rely on Freetype 2 building on host.

While at it, remove sed-editing of freetype-config that is no longer
necessary. The current version of freetype-config correctly identifies
prefix, exec_prefix, includedir and libdir.

Signed-off-by: Val Kulkov <val.kulkov@gmail.com>