Remove hard coding of ascii encoding when compiling SDK stubs

Hard coding the compiler to treat the Java files as if they
were ASCII is inconsistent with how Java is compiled everywhere
else in the Android build. This causes problems with the upgrade
to ICU 58 which adds copyright symbols in UTF-8 encoding in its
copyright comments.

This change has no discernable effect on the SDK generated from
the existing Java code.

Bug: 31328818
Test: Built the SDK with and without and compared the two.
Change-Id: Ied5ba2fa98e1e0ca6c265ba353b4091892170541

build/build_android_stubs.mk

@@ -55,7 +55,7 @@ $(full_target): $(stub_timestamp) $(framework_res_package)
 	$(hide) $(ACP) libcore/ojluni/NOTICE $(PRIVATE_CLASS_INTERMEDIATES_DIR)/NOTICES/ojluni-NOTICE
 	$(hide) find $(PRIVATE_SRC_DIR) -name "*.java" > \
         $(PRIVATE_INTERMEDIATES_DIR)/java-source-list
-	$(hide) $(TARGET_JAVAC) -source 1.8 -target 1.8 -encoding ascii -bootclasspath "" \
+	$(hide) $(TARGET_JAVAC) -source 1.8 -target 1.8 -bootclasspath "" \
 			-g -extdirs "" -d $(PRIVATE_CLASS_INTERMEDIATES_DIR) \
 			\@$(PRIVATE_INTERMEDIATES_DIR)/java-source-list \
 		|| ( rm -rf $(PRIVATE_CLASS_INTERMEDIATES_DIR) ; exit 41 )