Project health: remove temporal JDK 10 support in makefiles.
Project health: remove temporal JDK 10 support in makefiles.

PiperOrigin-RevId: 282058761

google/j2objc,lukhnos/j2objc,groschovskiy/j2objc,mirego/j2objc,google/j2objc,google/j2objc,groschovskiy/j2objc,mirego/j2objc,lukhnos/j2objc,lukhnos/j2objc,lukhnos/j2objc,lukhnos/j2objc,mirego/j2objc,google/j2objc,mirego/j2objc,google/j2objc,groschovskiy/j2objc,lukhnos/j2objc,groschovskiy/j2objc,groschovskiy/j2objc,google/j2objc,mirego/j2objc,groschovskiy/j2objc,mirego/j2objc