agx: Remove p_extract

It's now unused. We didn't have coalescing for it anyway, splits are the
preferred alternative.

Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/17198>

src/asahi/compiler/agx_opcodes.py

@@ -257,7 +257,6 @@ op("p_logical_end", _, dests = 0, srcs = 0, can_eliminate = False)
 
 op("p_combine", _, srcs = 4)
 op("p_split", _, srcs = 1, dests = 4)
-op("p_extract", _, srcs = 1, imms = [COMPONENT])
 
 # Phis are special-cased in the IR as they (uniquely) can take an unbounded
 # number of source.