Bug 1832209 - Remove a bunch of unused add_old_configure_assignment. r=firefox-build-system-reviewers,ahochheiden

- Last use of CROSS_COMPILE was removed in bug 1460620,
- Last use of EARLY_BETA_OR_EARLIER was removed in bug 1603834,
- Last use of RELEASE_OR_BETA was removed in bug 1670948,
- Last use of MOZILLA_VERSION was removed in bug 1745838,
- Last use of GNU_AS was removed in bug 1635764,
- Last use of AR was removed in bug 1638193,
- Last use of PKG_CONFIG was removed in bug 1747775,
- Last use of MOZ_DMD was removed in bug 1747970,
- Last use of NSPR_CFLAGS and NSS_CFLAGS were removed in bug 1722652,
- Last use of MOZ_PROFILING was removed in bug 1640578,
- Last use of USE_FC_FREETYPE was removed in bug 1747325,
- Last use of MOZ_FMP4 was removed in bug 1382930,
- Last use of MOZ_WEBSPEECH was removed in bug 1295480,
- MOZ_ASAN_REPORTER doesn't seem to have ever been used,
- Last use of MOZ_THUMB2 and ANDROID_CPU_ARCH were removed in bug 1814802,
- Last use of ARM_ARCH was removed in bug 1747753,

Differential Revision: https://phabricator.services.mozilla.com/D177581