Deduplicate test expectation data in a different way

The test collects expected APEX package names from listing /apex by a
shell command. The shell command also tries to remove the noise
(normally an APEX has two entires, see below).

$ ls -d /apex/*/
  /apex/com.android.adbd/
  /apex/com.android.adbd@340815002/
  ...
  /apex/com.google.mainline.primary.libs@340716000/
  /apex/sharedlibs/

The test used to deduplicate by filtering out '@'. But apparently an
(DLCA) APEX only has one entry with '@'.

With this change, the shell command removes '@\d+' then deduplicate the
strings.

Bug: 288551133
Test: BinaryTransparencyHostTest#testCollectAllApexInfo
Change-Id: I4bc3e8226dd7790aa276ac5dfad7371c60046384