Fix build without INDI
Without INDI present I get the following error:
"x86_64-pc-linux-gnu-ld: ../lib/libKStarsLib.a(robuststatistics.cpp.o):
in function Mathematics::GSLHelpers::gslMedianFromSortedData( double const*, unsigned long, unsigned long)': .../work/kstars-3.6.5/kstars/auxiliary/gslhelpers.h:306: undefined reference to
gsl_stats_median_from_sorted_data'"
That is the case because Mathematics::RobustStatistics is used unconditionally, which pulls in gslhelpers and the need to link with GSL.
Also drop the duplicate linking of KF5::Notifications, KStarsLib already links to it in the NOT ANDROID case.