[lldb] Remove obsolete Android-specific definitions

Bionic's <sys/procfs.h> defines the necessary symbols.  Remove the
specialization for Android and the now-unnecessary include of
<sys/ptrace.h>.  This also helps resolve issues when building the
x86/x86_64 lldb-server for Android.

Curiously, the default branch to include <sys/procfs.h> doesn't seem
necessary on Linux.  I'll remove it and add it back if it breaks other
builders.

Differential Revision: https://reviews.llvm.org/D132514