remove admin panel & related code (#2584) #302

Job	Run time
Apache2 tests on Linux	4m 0s
Nginx tests on Linux	3m 15s
C++ tests on Linux	2m 38s
C++ tests on macOS	3m 59s
Apache2 tests on macOS	2m 19s
Nginx tests on macOS	2m 37s
Nginx dynamic module tests on Linux	1m 8s
Homebrew packaging tests	8m 25s
Node.js tests on Linux	23s
Nginx dynamic module tests on macOS	1m 29s
Node.js tests on macOS	24s
Ruby tests on Linux	1m 8s
Passenger Standalone tests on Linux	3m 33s
Ruby tests on macOS	1m 8s
Passenger Standalone tests on macOS	4m 47s
Source packaging tests	25s
	41m 38s

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