Remove unused flags for arm64-v8a

Through using ndk-build, -Wno-unused-command-line-argument is passed in
somewhere in the pipeline and hides this warning.

The warning can be turned on with:
APP_CPPFLAGS := -Wunused-command-line-argument ...

and then when building, you can see:
C/C++: clang++: warning: argument unused during compilation: '-mfloat-abi=softfp' [-Wunused-command-line-argument]
C/C++: clang++: warning: argument unused during compilation: '-mfpu=neon' [-Wunused-command-line-argument]
C/C++: clang++: warning: argument unused during compilation: '-maes' [-Wunused-command-line-argument]

These are unused because both floating-point and NEON are required in
all standard ARMv8 implementations. [1] [2]

[1] https://developer.arm.com/documentation/den0024/a/AArch64-Floating-point-and-NEON

[2] https://stackoverflow.com/a/29891469

java/jni/Android.mk

@@ -16,8 +16,7 @@ ifeq ($(TARGET_ARCH_ABI),x86_64)
     LOCAL_CXXFLAGS := -maes -mpclmul -msse3 -msse4.1
 endif
 ifeq ($(TARGET_ARCH_ABI),arm64-v8a)
-    LOCAL_ARM_NEON := true
-    LOCAL_CXXFLAGS := -march=armv8-a+crypto -mfloat-abi=softfp -mfpu=neon -maes
+    LOCAL_CXXFLAGS := -march=armv8-a+crypto
 endif
 
 # ZeroTierOne SDK source files