Delete get_prop(su, ...) rules

It is unnecessary to use get_prop() rules for the su domain. The
su domain is always in permissive mode [1] and not subject to SELinux
enforcement. It's also possible these rules were added to avoid SELinux
denial log spam from showing up, however, there are already dontaudit
rules in place [2] to prevent this.

Delete the unnecessary rules.

[1] https://android.googlesource.com/platform/system/sepolicy/+/96b62a60c2ccae777fdcabe7d2ed28b52056860b/private/su.te#19
[2] https://android.googlesource.com/platform/system/sepolicy/+/96b62a60c2ccae777fdcabe7d2ed28b52056860b/public/su.te#42

Test: policy compiles
Change-Id: I5913f360738725bf915f0606d381029b9ba4318f