external-sourcery-toolchain: Avoid conflict with lttng-tools

external toolchain shouldn't be shipping lttng stuff unless a
preference is explicitly set indicating it should be used
instead. Drop bits conflicting with those being provided
by lttng-tools.

Signed-off-by: Yasir-Khan <yasir_khan@mentor.com>
Merge pull request #45 from Yasir-Khan/lttng-conflict

external-sourcery-toolchain: Avoid conflict with lttng-tools