Remove unnecessary minSdkVersion in app CTS test manifest

This seems to be accidentally added in ag/746767. Removing this as it is not
needed. As-is, it is blocking androidx minSdkVersion bump to API 19.

Bug: 307291543
Change-Id: I941c7f6a05af5e2fb3e4f0498d09df69cbd1d855
Test: None
1 file changed