Relicense librseq to MIT

Relicense librseq to MIT

For simplicity, relicense all librseq (header files, library
implementation and tests) to MIT.

Header files were previously dual-licensed LGPL2.1/MIT, which is
somewhat redundant with MIT.

rseq.c was licensed under LGPL2.1. Relicence it to MIT to facilitate its
integration into statically built applications.

In order to facilitate eventual code sharing between tests and the
library implementation, relicence the tests from LGPL2.1 to MIT.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Change-Id: Ie819e1527ddffce64e4fe76024e2728e8a723c25