Unlist libunwind as a critical component

Virtually nothing uses libunwind, and no one should start using it, so
it's unlikely to be critical.

(Code should use libunwindstack.so to collect backtraces, and it should
use libc.so's _Unwind_* APIs for C++ exception handling unwinding.)

Test: build Android
Change-Id: I81882a4634ff4d397abe8a7cf5ff15a22a3eed2f
Merged-In: I81882a4634ff4d397abe8a7cf5ff15a22a3eed2f
(cherry picked from commit 9355aeba79)

core/line_coverage.mk

@@ -47,7 +47,6 @@ critical_components_shared := \
 	libinputflinger \
 	libopus \
 	libstagefright \
-	libunwind \
 	libvixl:com.android.art.debug
 
 # Use the intermediates directory to avoid installing libraries to the device.