remove LDA_X from optb88

parser/parser-quantum-espresso/QuantumEspressoXC.py

@@ -702,6 +702,9 @@ EXCHANGE_GRADIENT_CORRECTION = [
         'xc_terms': [{
             'XC_functional_name': "GGA_X_OPTB88_VDW",
         }],
+        'xc_terms_subtract': [{
+            'XC_functional_name': 'LDA_X',
+        }],
         'xc_section_method': {
             'x_qe_xc_igcx_name':       "obk8",
             'x_qe_xc_igcx_comment':    "optB88  exchange",

test/xc_functionals/refactor_test/testuite-xc.ref.log

@@ -134,9 +134,6 @@ qe_xc: 0.00 OPTBK88 ( 1  4 23  1 0 0)
   },
   {
     "XC_functional_name": "LDA_C_PW"
-  },
-  {
-    "XC_functional_name": "LDA_X"
   }
 ]
 qe_xc: 0.00 VDW-DF2 ( 0 413 0 2)
@@ -583,9 +580,6 @@ qe_xc: 0.00 VDW-DF-OBK8 ( 1  4 23  0 1 0)
   {
     "XC_functional_name": "LDA_C_PW"
   },
-  {
-    "XC_functional_name": "LDA_X"
-  },
   {
     "XC_functional_name": "x_qe_VDW_DF1"
   }