Remove 26.0 and 27.0 compat support

Treble doesn't support T system + O vendor, so removing 26.0 (N) and
27.0 (O) prebuilts and compat files.

Bug: 207815515
Test: build
Change-Id: Ie12737cc5ca8725caf834d9bf1bdfe840ac516c0
diff --git a/core/config.mk b/core/config.mk
index 7c93610..6f89853 100644
--- a/core/config.mk
+++ b/core/config.mk
@@ -833,8 +833,6 @@
 
 # A list of SEPolicy versions, besides PLATFORM_SEPOLICY_VERSION, that the framework supports.
 PLATFORM_SEPOLICY_COMPAT_VERSIONS := \
-    26.0 \
-    27.0 \
     28.0 \
     29.0 \
     30.0 \