build: fix android build, fix symbol redefinition

linux-core defines uv_get_free_memory() and uv_get_total_memory() so
don't include sysinfo-memory.c too. The cmake and autotools builds
don't do so either.

PR-URL: https://github.com/libuv/libuv/pull/2542
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Saúl Ibarra Corretgé <saghul@gmail.com>

uv.gyp

@@ -264,7 +264,6 @@
             'src/unix/random-getrandom.c',
             'src/unix/random-sysctl-linux.c',
             'src/unix/sysinfo-loadavg.c',
-            'src/unix/sysinfo-memory.c',
           ],
           'link_settings': {
             'libraries': [ '-ldl' ],