Bug 1609422 - Clean up an old rustc version check for pgo r=firefox-build-system-reviewers,chmanchester

We require rustc 1.39 nowadays.

Differential Revision: https://phabricator.services.mozilla.com/D60008

--HG--
extra : moz-landing-system : lando

build/moz.configure/lto-pgo.configure

@@ -136,10 +136,6 @@ def moz_pgo_rust(pgo, profile_use, profile_generate, c_compiler, rustc):
     if c_compiler.type == 'gcc':
         die('Cannot use cross-language PGO with GCC.')
 
-    # PGO is not stable prior to 1.37
-    if rustc.version < Version('1.37'):
-        die('Cannot use cross-language PGO with Rust version %s.' % rustc.version)
-
     return True
 
 set_config('MOZ_PGO_RUST', moz_pgo_rust)