Bug 1407432 - Remove ucx$inetdef.h from system headers; r=froydnj,ted

This is no longer used in the tree, and the $ will get eaten somewhere
along the way on the path from moz.build to the python invocation by
make despite being shell_quoted.

MozReview-Commit-ID: 5mwWQYDn8Nf

--HG--
extra : source : ffe9aed0944f57e329ee279f5b14266d5c4069a2

config/system-headers

@@ -1110,7 +1110,6 @@ UAttachments.h
 ucontext.h
 uconv.h
 UCursor.h
-ucx$inetdef.h
 UDebugging.h
 UDesktop.h
 UDrawingState.h