[lldb] Prefer executable files from sysroot over files from local filesystem

Summary:
In D49685 sysroot behaviour was partially fixed. But files from local filesystem with same path still has priority over files from sysroot.

This patch fixes it by removing fallback to local filesystem from RemoteAwarePlatform::GetModuleSpec(). It is not actually required because higher level code do such fallback itself. See, for example, resolver in Platform::GetSharedModule().

Reviewers: labath, clayborg, EugeneBi

Reviewed By: labath

Subscribers: lldb-commits

Tags: #lldb

Differential Revision: https://reviews.llvm.org/D77529