Remove dependency to real NotoColorEmoji.ttf.

NotoColorEmoji.ttf has 'by-exception-only' license and should not have
been depended by vts.
This CL swaps it with a fake NotoColorEmoji.ttf font.
testdata/NotoColorEmoji.ttx is based on
cts/tests/tests/text/assets/fonts/samplefont.ttx

Bug: 191914223
Test: atest UpdatableSystemFontTest
Change-Id: If5f57471b492cae1eb35f6d4a4ac0054270b23a3