Bug 1253456 - Disable rust on win32 builds. r=mshal

Until we can address the sse2 code generation issue,
disable rust on win32 nightly, beta, and release builds.

Leave it enabled in debug builds for testing convenience.

browser/config/mozconfigs/win32/beta

@@ -13,6 +13,4 @@ mk_add_options MOZ_PGO=1
 ac_add_options --enable-official-branding
 ac_add_options --enable-verify-mar
 
-. "$topsrcdir/build/mozconfig.rust"
-
 . "$topsrcdir/build/mozconfig.common.override"

browser/config/mozconfigs/win32/nightly

@@ -6,7 +6,5 @@ ac_add_options --enable-verify-mar
 
 ac_add_options --with-branding=browser/branding/nightly
 
-. "$topsrcdir/build/mozconfig.rust"
-
 . "$topsrcdir/build/mozconfig.common.override"
 . "$topsrcdir/build/mozconfig.cache"

browser/config/mozconfigs/win32/release

@@ -19,6 +19,4 @@ ac_add_options --enable-verify-mar
 # defines.sh during the beta cycle
 export BUILDING_RELEASE=1
 
-. "$topsrcdir/build/mozconfig.rust"
-
 . "$topsrcdir/build/mozconfig.common.override"