Revert "[lldb] Make CommandInterpreter's execution context the same as debugger's one."

This reverts commit a01b26fb51, because it
breaks the "finish" command in some way -- the command does not
terminate after it steps out, but continues running the target. The
exact blast radius is not clear, but it at least affects the usage of
the "finish" command in TestGuiBasicDebug.py. The error is *not*
gui-related, as the same issue can be reproduced by running the same
steps outside of the gui.

There is some kind of a race going on, as the test fails only 20% of the
time on the buildbot.

lldb/test/API/python_api/debugger/main.cpp

@@ -1,9 +0,0 @@
-// This simple program is to test the lldb Python API SBDebugger.
-
-int func(int val) {
-    return val - 1;
-}
-
-int main (int argc, char const *argv[]) {
-    return func(argc);
-}