Remove km_MH locale from mainline

This doesn't appear to be a real locale. The interpretation would be
khmer spoken in the Marshall Islands, which doesn't appear to be a thing.
The locale doesn't appear in https://lh.2xlibre.net/locales/ or
frameworks/base/core/res/res/values/locale_config.xml.

It might have been a typo when it was introduced in internal change
I78d91916fdbb04502466c26bf7d160fe679aaa31.

Test: make
Change-Id: Id1deebdd8ad2a5601c15b84e010be766b3a951e9
diff --git a/target/product/mainline_system.mk b/target/product/mainline_system.mk
index c41e1d7..639c639 100644
--- a/target/product/mainline_system.mk
+++ b/target/product/mainline_system.mk
@@ -97,7 +97,7 @@
 # Enable dynamic partition size
 PRODUCT_USE_DYNAMIC_PARTITION_SIZE := true
 
-PRODUCT_LOCALES := en_US af_ZA am_ET ar_EG as_IN az_AZ be_BY bg_BG bn_BD bs_BA ca_ES cs_CZ da_DK de_DE el_GR en_AU en_CA en_GB en_IN es_ES es_US et_EE eu_ES fa_IR fi_FI fr_CA fr_FR gl_ES gu_IN hi_IN hr_HR hu_HU hy_AM in_ID is_IS it_IT iw_IL ja_JP ka_GE kk_KZ km_KH ko_KR ky_KG lo_LA lt_LT lv_LV km_MH kn_IN mn_MN ml_IN mk_MK mr_IN ms_MY my_MM ne_NP nb_NO nl_NL or_IN pa_IN pl_PL pt_BR pt_PT ro_RO ru_RU si_LK sk_SK sl_SI sq_AL sr_Latn_RS sr_RS sv_SE sw_TZ ta_IN te_IN th_TH tl_PH tr_TR uk_UA ur_PK uz_UZ vi_VN zh_CN zh_HK zh_TW zu_ZA en_XA ar_XB
+PRODUCT_LOCALES := en_US af_ZA am_ET ar_EG as_IN az_AZ be_BY bg_BG bn_BD bs_BA ca_ES cs_CZ da_DK de_DE el_GR en_AU en_CA en_GB en_IN es_ES es_US et_EE eu_ES fa_IR fi_FI fr_CA fr_FR gl_ES gu_IN hi_IN hr_HR hu_HU hy_AM in_ID is_IS it_IT iw_IL ja_JP ka_GE kk_KZ km_KH ko_KR ky_KG lo_LA lt_LT lv_LV kn_IN mn_MN ml_IN mk_MK mr_IN ms_MY my_MM ne_NP nb_NO nl_NL or_IN pa_IN pl_PL pt_BR pt_PT ro_RO ru_RU si_LK sk_SK sl_SI sq_AL sr_Latn_RS sr_RS sv_SE sw_TZ ta_IN te_IN th_TH tl_PH tr_TR uk_UA ur_PK uz_UZ vi_VN zh_CN zh_HK zh_TW zu_ZA en_XA ar_XB
 
 PRODUCT_NAME := mainline_system
 PRODUCT_BRAND := generic