package/graphite2: fix static install

Don't install an incorrect libtool file when building a static library
to fix the following build failure with harfbuzz:

arm-linux-g++.br_real: error: /home/buildroot/autobuild/run/instance-3/output-1/host/arm-buildroot-linux-uclibcgnueabi/sysroot/usr/lib/libgraphite2.so: No such file or directory
make[5]: *** [main] Error 1

Fixes:
 - http://autobuild.buildroot.org/results/9ebe1d11e80755d59190ef2aae82bbba5cc45e44



Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>