TComPicYuv: replace xExtendPicCompBorder with an optimized function

We've had a primitive for the side borders for some time, it just wasn't hooked
up.  This function never should have been a method of that class.

--HG--
extra : rebase_source : bb51c5269cf4c53ae59ae738cbb3c04680def16a
lowres: nits

--HG--
extra : rebase_source : 8f19076cb104f7e2b2bbc34cf8c42f0f4f766f58
pic: mask impossible input bits

--HG--
extra : rebase_source : fdb3dc9eed52e433232b07fd601501ca69d08653
pic: use C style comments

--HG--
extra : rebase_source : 3e443c38a3a8f8856f2eb66eccfa451c5a9551d1
cleanup unused
cleanup AMVP related
slicetype: pass bools as bool literals

--HG--
extra : rebase_source : 03f89dcf774250b84154e0354acc95c9aebd3abf