Revert "configure: Switch debug build from -O0 to -Og"

This reverts commit 7e68ed6a5d. With -Og
simple 'gdb build/debug/scylla -ex start' shows the function parameters
as "optimized out" while with -O0 they display fine. This applies to
all variables, not just main's parameters.

Bisect revealed that this behavior started with the reverted commit; it's
not due to a later toolchain update.

Fixes #14196.

Closes #14197

configure.py

@@ -286,7 +286,8 @@ modes = {
         'cxx_ld_flags': '',
         'stack-usage-threshold': 1024*40,
         # -fasan -Og breaks some coroutines on aarch64, use -O0 instead
-        'optimization-level': ('0' if platform.machine() == 'aarch64' else 'g'),
+        # also, -Og was seen to make all variables "optimized out"
+        'optimization-level': '0',
         'per_src_extra_cxxflags': {},
         'cmake_build_type': 'Debug',
         'can_have_debug_info': True,