Disable TypefaceTest#testSetSystemFontMap

The Typeface#setSystemFontMap no longer cannot be called multiple
times.

Bug: 436439539
Test: atest TypefaceTest
Flag: com.android.text.flags.do_not_overwrite_static_final_field
Change-Id: Ib58d22749ef11fbc629d4d5b06bfbccad4994641