Removed redundat UIAutomator killing during init (#265)

Removed killing any existing UIAutomator2 processes running on device
during phase of UIAutomator2Server initialization, which is not required
at that point, due to possibility of reinstallation apks. Moreover
processes are killed eitherway on the begging of session startup.

lib/driver.js

@@ -396,9 +396,6 @@ class AndroidUiautomator2Driver extends BaseDriver {
     });
     this.proxyReqRes = this.uiautomator2.proxyReqRes.bind(this.uiautomator2);
 
-    // killing any uiautomator existing processes
-    await this.uiautomator2.killUiAutomatorOnDevice();
-
     await this.uiautomator2.installServerApk(this.opts.uiautomator2ServerInstallTimeout);
   }