lttng-babeltrace: make available for all C libraries

Due to posix_fallocate() being unavailable in uClibc 0.9.33,
lttng-babeltrace was marked as available only for uClibc snapshot and
glibc. However:

 - lttng-babeltrace builds fine with musl
 - lttng-babeltrace builds fine with uClibc-ng
 - we're going to get rid of uClibc 0.9.33 support
 - the only toolchain left with an old uClibc version is the Blackfin
   Analog Devices toolchain, and lttng-babeltrace cannot be enabled on
   non-MMU platforms

Conclusion: We can enable lttng-babeltrace on all C libraries, and no
longer require any condition. This commit adjusts the lttng-babeltrace
package accordingly.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Tested-by: Romain Naour <romain.naour@gmail.com>
Reviewed-by: Romain Naour <romain.naour@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>