Android: Restore searching PATH for executables

Since commit a7f41a7ee4 (Android: Fix find_* search order within NDK for
unified toolchains, 2020-10-13, v3.20.0-rc1~610^2), we turn off
`CMAKE_FIND_USE_SYSTEM_ENVIRONMENT_PATH`.  This breaks `find_program`
searching `PATH` for host executables.  Fortunately, the setting turns
out not to be necessary, perhaps since commit cbc51a8be3 (Android:
restructure android search paths, 2020-11-06, v3.20.0-rc1~509^2).
Without it, none of NDK tests fail, so remove it to restore pre-3.20
behavior.

Fixes: #22634

Modules/Platform/Android-Initialize.cmake

@@ -56,11 +56,6 @@ if(CMAKE_ANDROID_NDK_TOOLCHAIN_UNIFIED)
     set(CMAKE_FIND_ROOT_PATH_MODE_PACKAGE ONLY)
   endif()
 
-  # Don't search paths in PATH environment variable.
-  if(NOT DEFINED CMAKE_FIND_USE_SYSTEM_ENVIRONMENT_PATH)
-    set(CMAKE_FIND_USE_SYSTEM_ENVIRONMENT_PATH OFF)
-  endif()
-
   # Allows CMake to find headers in the architecture-specific include directories.
   set(CMAKE_LIBRARY_ARCHITECTURE "${CMAKE_ANDROID_ARCH_TRIPLE}")