Remove unused macros

Reported by clang:
xcompmgr.c:159:9: warning: macro is not used [-Wunused-macros]
 #define TRANS_OPACITY   0.75
         ^
xcompmgr.c:166:9: warning: macro is not used [-Wunused-macros]
 #define SHADOWS         1
         ^
xcompmgr.c:167:9: warning: macro is not used [-Wunused-macros]
 #define SHARP_SHADOW    0
         ^

Signed-off-by: Alan Coopersmith <alan.coopersmith@oracle.com>
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