Revert IgnOGRE Windows fix, it breaks downstream libraries

[chapulina]

This was introduced in #206, and now trying to compile ign-gui3 against it I get:

CMake Error at src/plugins/CMakeLists.txt:29 (add_library):
  Target "Grid3D" links to target "IgnOGRE::IgnOGRE" but the target was not               
  found.  Perhaps a find_package() call is missing for an IMPORTED target, or
  an ALIAS target is missing?       
Call Stack (most recent call first): 
  src/plugins/CMakeLists.txt:77 (ign_gui_add_library)
  src/plugins/grid_3d/CMakeLists.txt:1 (ign_gui_add_plugin)
                                    
                                     
CMake Error at src/plugins/CMakeLists.txt:29 (add_library):
  Target "Scene3D" links to target "IgnOGRE::IgnOGRE" but the target was not
  found.  Perhaps a find_package() call is missing for an IMPORTED target, or
  an ALIAS target is missing?            
Call Stack (most recent call first):  
  src/plugins/CMakeLists.txt:77 (ign_gui_add_library)
  src/plugins/scene3d/CMakeLists.txt:1 (ign_gui_add_plugin)  

I originally did it to fix a Windows warning. Let's see how CI comes back. If Windows is still complaining, we may need a different fix.

[codecov]

Codecov Report

Merging #215 (2e99ff6) into ign-rendering3 (64714e5) will increase coverage by 0.00%.
The diff coverage is n/a.

@@               Coverage Diff               @@
##           ign-rendering3     #215   +/-   ##
===============================================
  Coverage           50.34%   50.35%           
===============================================
  Files                 129      129           
  Lines               11782    11782           
===============================================
+ Hits                 5932     5933    +1     
+ Misses               5850     5849    -1     

Impacted Files	Coverage Δ
...e/ignition/rendering/base/BaseGaussianNoisePass.hh	100.00% <0.00%> (+3.33%)	⬆️

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[j-rivero]

No warnings on Windows. Good to go.