Remove enabled flag high_contrast_text_luminance

The flag was relased in 24 Q3. It has been enabled more than 6 month.

NO_IFTTT=New IFTTT tags

Bug: 384793956
Flag: EXEMPT removing com.android.graphics.hwui.flags.high_contrast_text_luminance
Test: atest frameworks/base/core/tests/coretests/src/android/text/LayoutTest.java
Test: atest cts/tests/tests/uirendering/src/android/uirendering/cts/testclasses/TextViewHighContrastTextTests.kt
Change-Id: I86255f2a1ea5bb5a95ad2d1714d239141ab5bd74