Revert "Master is now S"

This reverts commit de005e83f7d5d09c9bc53c2a6ee2a92d10a38610.

Reason for revert: BuildCompat.isAtLeastR is broken: b/154661881

Change-Id: I4284c636ae26b45c0e7c715215778ef00e7bbab1
diff --git a/core/version_defaults.mk b/core/version_defaults.mk
index 00befa4..6d3fcae 100644
--- a/core/version_defaults.mk
+++ b/core/version_defaults.mk
@@ -39,9 +39,9 @@
   include $(INTERNAL_BUILD_ID_MAKEFILE)
 endif
 
-DEFAULT_PLATFORM_VERSION := SP1A
-MIN_PLATFORM_VERSION := SP1A
-MAX_PLATFORM_VERSION := SP1A
+DEFAULT_PLATFORM_VERSION := RP1A
+MIN_PLATFORM_VERSION := RP1A
+MAX_PLATFORM_VERSION := RP1A
 
 ALLOWED_VERSIONS := $(call allowed-platform-versions,\
   $(MIN_PLATFORM_VERSION),\
@@ -94,7 +94,6 @@
 # These are the current development codenames, if the build is not a final
 # release build.  If this is a final release build, it is simply "REL".
 PLATFORM_VERSION_CODENAME.RP1A := R
-PLATFORM_VERSION_CODENAME.SP1A := S
 
 ifndef PLATFORM_VERSION_CODENAME
   PLATFORM_VERSION_CODENAME := $(PLATFORM_VERSION_CODENAME.$(TARGET_PLATFORM_VERSION))