Expand clip triangle to remove hairline gaps around signal triangle.

This CL also simplifies the signal level: it needed to be
expanded to ensure it entirely covers the clip, so now it's
just a big rectangle from (0,0) --> (X, 24) for an
appropriate value of X.

Fixes: 339440394
Test: atest -c SystemIconsScreenshotTest
Test: presubmits
Flag: n/a
Change-Id: Ie59282fafda7ca4ecb101e26bba1aabb6517a6d1