Remove check on "is_netcdf" from non-existent libncdf.a in ropp_{pp, fm, 1dvar} configure.ac

[Ian Culverwell]

Dave Offiler writes:

One slight oddity in configuring ropp_pp ropp_fm & ropp_1dvar:

checking for message of the ropp_utils library... yes checking for
nf_inq_ncid of the hdf5 library... yes checking for nf_open of the 
netcdf library... yes
checking for is_netcdf of the ncdf library... no            <<<<<<<
checking for is_netcdf of the ropp_io library... yes checking for
ropp_io_init_l1atype of the ropp_io library... (cached) yes

e.g. in ropp_pp/configure.ac:
  CM_CHECK_LIB(ncdf, is_netcdf, -lncdf)

I don't think there's any such library as libncdf.a (possible
legacy of Christian's 'ncdf' API which has been part of ropp_io 
since the beginning? Or for a really old version of netCDF (v3.x)?) 
Clearly is_netCDF() *is* found in libropp_io.a, so in practice not
a problem, but I'm not sure if this (any more) is a valid test to
do... But as it does no harm. it can be left in place for ROPP-8.

Consider removing these checks on libncdf.a at ROPP9.0.

[Ian Culverwell]

Defer to ROPP10.0.

[warrick]

Took a look at this for ROPP10.0, and decided to leave as it is. At the moment it simply looks for is_netcdf in libncdf.a:

CM_CHECK_LIB(ncdf,     is_netcdf,   -lncdf)

which it doesn't find. It then looks for is_netcdf in ropp_io, which it does find:

CM_CHECK_LIB(ropp_io, is_netcdf,            -lropp_io)

so the checking is fine how it is. It is best not to tamper with the Makefiles and configure files.