[LLDB] dotest.py set selected_platform on remote connection

This patch fixes a bug in dotest.py where lldb.selected_platform was
being set to host platform even after a successful connection to a
remote platform via platform url. This patch fixes this behavior and
sets selected_platform to remote_platform after a successful connection.

This patch also removes target_platform variable from run_suite.

Reviewed By: JDevlieghere

Differential Revision: https://reviews.llvm.org/D105060

lldb/packages/Python/lldbsuite/test/dotest.py

@@ -929,6 +929,7 @@ def run_suite():
             err = lldb.remote_platform.ConnectRemote(platform_connect_options)
             if err.Success():
                 print("Connected.")
+                lldb.selected_platform = lldb.remote_platform
             else:
                 print("error: failed to connect to remote platform using URL '%s': %s" % (
                     configuration.lldb_platform_url, err))
@@ -958,9 +959,6 @@ def run_suite():
     # Note that it's not dotest's job to clean this directory.
     lldbutil.mkdir_p(configuration.test_build_dir)
 
-    from . import lldbplatformutil
-    target_platform = lldbplatformutil.getPlatform()
-
     checkLibcxxSupport()
     checkLibstdcxxSupport()
     checkWatchpointSupport()