Drop support for Arm (Armv7 should be default)

[paulrouget]

@MortimerGoro mentioned in #21851:

We can drop normal "arm", it's already deprecated. There aren't Android 4+ devices which support armeabi but not armeabi-v7a, so we can safely drop armeabi and save some compilation work & upload bandwidth. We can remove armeabi also from Servo cloud compilation tests if it's still there.

[SimonSapin]

Do we have any support to drop? It looks like we’re already building for ARMv7:

servo/python/servo/command_base.py

Lines 298 to 299 in 57053e0

	# Set default android target
	self.handle_android_target("armv7-linux-androideabi")

[paulrouget]

I haven't really looked. What about

servo/python/servo/package_commands.py

Line 223 in 57053e0

else:

or support/android/fakeld/fake-ld-arm.sh or the armr reference in the different build.gradle files?