Remove FindO2.cmake now that O2 uses modern CMake (QC-220) (#217)

Author: Barthelemy

CMakeLists.txt

@@ -94,7 +94,7 @@ find_package(MySQL)
 find_package(Common REQUIRED)
 find_package(InfoLogger REQUIRED)
 find_package(ms_gsl MODULE REQUIRED)
-find_package(O2 MODULE REQUIRED)
+find_package(O2 CONFIG REQUIRED)
 find_package(CURL REQUIRED)
 find_package(GLFW NAMES glfw3 CONFIG)
 find_package(FairMQ REQUIRED)