asm: update and rename built-in functions

eBPF helpers are added frequently, so we should make updating the list
simple. Remove the (duplicate, probably incorrect) documentation and
re-generate the new list of functions.

Author: lmb

asm/alu_string.go

@@ -10,7 +10,7 @@ func TestDSL(t *testing.T) {
 		have Instruction
 		want Instruction
 	}{
-		{"Call", MapLookupElement.Call(), Instruction{OpCode: 0x85, Constant: 1}},
+		{"Call", FnMapLookupElem.Call(), Instruction{OpCode: 0x85, Constant: 1}},
 		{"Exit", Return(), Instruction{OpCode: 0x95}},
 		{"LoadAbs", LoadAbs(2, Byte), Instruction{OpCode: 0x30, Constant: 2}},
 		{"Store", StoreMem(RFP, -4, R0, Word), Instruction{