gcc-runtime: Remove libgfortran data from receipe

Remove libgfortran packages from PACKAGES list as long as libgfortran
has separate receipe since commit

5bde5d9b39ea67f19a1a6aedd0c08c6cfedcbe5f
gcc: Allow fortran to build successfully in 4.8

Otherwise, when fortran support will be enabled in the compiler, both
lingfortran and gcc-runtime receipes will create the same files and will
try to install them. This will cause errors:

ERROR: The recipe libgfortran is trying to install files into a shared
area when those files already exist. Those files and their manifest
location are: ...
Please verify which recipe should provide the above files.

(From OE-Core rev: 872342fa)

Signed-off-by: Daniel Dragomir <daniel.dragomir@windriver.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
Signed-off-by: Armin Kuster <akuster808@gmail.com>