Android: Revert setting LINUX variable on Android target systems

Since commit 62cd3904bf (variable: Set LINUX variable on Linux target
systems, 2022-08-10, v3.25.0-rc1~320^2), the `Platform/Android` module
inherits the `LINUX` variable setting from `Platform/Linux`.  While
Android may use a Linux kernel, `CMAKE_SYSTEM_NAME` is not `Linux`, and
the platform does not follow conventions of most Linux distributions.

Fixes: #24196