eng builds: dexpreopt: stop explicitly removing minidebuginfo

This special-casing is actively unhelpful nowadays, as it breaks
callstack unwinding and symbolisation by tools that work using the
on-device debug info (e.g. perfetto's profilers). It's also highly
surprising that eng builds have less debug info than userdebug/user.

As far as I can tell, the history behind this case is (with some
internal-only references as the context is in the review comments): the
minidebuginfo was originally rolled out in device-specific makefiles
(e.g. ag/2433691). Eng builds were excluded, presumably due to time/size
concerns for rebuild+resync workflow, as well as the assumption that
engineers using eng builds already have the necessary debug info
off-device. Later, as some more makefile variables were introduced, the
conversation in ag/990059 shows that the overheads were no longer a
concern, and the last patchset generalised the option to include eng
builds. However at a later point, during device-specific makefile
cleanup, the eng-exclusion got restored: ag/2455645. This then ended up
in the makefile->soong transition, leaving us with the current special
casing that is undesireable.

Checking things with an internal master build on my workstation:
dexpreopting system services is 10s regardless of this minidebuginfo
flag, and the resulting odex size is 37MB vs 38MB. Overall, I only see 4
dexpreopt invocations as part of a local build, so the effect of this
patch should be negligible.

Bug: 194835631
Change-Id: I80de75a84259c056cdae0696fe611afe7e0162f5

dexpreopt/dexpreopt.go

@@ -430,11 +430,6 @@ func dexpreoptCommand(ctx android.PathContext, globalSoong *GlobalSoongConfig, g
 		}
 	}
 
-	// Never enable on eng.
-	if global.IsEng {
-		debugInfo = false
-	}
-
 	if debugInfo {
 		cmd.Flag("--generate-mini-debug-info")
 	} else {