xfsprogs: remove comment about uClibc specific options

xfsprogs: remove comment about uClibc specific options

xfsprogs now builds fine with Buildroot default uClibc configuration, so
there is no point in having a specific comment: we don't have this for
any other package, and it's basically impossible to maintain.

UCLIBC_SV4_DEPRECATED is still disabled in the Buildroot default uClibc
configuration, but xfsprogs builds fine without it.

UCLIBC_HAS_OBSOLETE_BSD_SIGNAL is now enabled in the Buildroot default
uClibc configuration.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>