Stop plants from creating xenomicrobes, nanomachines and tuberculosis (#56939)

My finger slipped and now these reagents have the equivalent of
can_synth = TRUE so uh that may not be very good

code/modules/reagents/chemistry/reagents/other_reagents.dm

@@ -1206,7 +1206,6 @@
 	name = "Nanomachines"
 	description = "Microscopic construction robots."
 	color = "#535E66" // rgb: 83, 94, 102
-	chemical_flags = REAGENT_CAN_BE_SYNTHESIZED
 	taste_description = "sludge"
 	penetrates_skin = NONE
 
@@ -1219,7 +1218,6 @@
 	name = "Xenomicrobes"
 	description = "Microbes with an entirely alien cellular structure."
 	color = "#535E66" // rgb: 83, 94, 102
-	chemical_flags = REAGENT_CAN_BE_SYNTHESIZED
 	taste_description = "sludge"
 	penetrates_skin = NONE
 
@@ -1232,7 +1230,6 @@
 	name = "Tubercle bacillus Cosmosis microbes"
 	description = "Active fungal spores."
 	color = "#92D17D" // rgb: 146, 209, 125
-	chemical_flags = REAGENT_CAN_BE_SYNTHESIZED
 	taste_description = "slime"
 	penetrates_skin = NONE
 	ph = 11