Englishify comment wording

Switch to using the English word here rather than using a verbified
function name.

The full word still fits within a single comment line, so it's probably
better just to use that instead of trying to shorten it, which might
cause confusion.

Author: Rafia Sabih <rafia.pghackers@gmail.com>
Discussion: https://postgr.es/m/CA+FpmFe7LnRF2NA_QfARjkSWme4mNt+Udwbh2Yb=zZm35Ji31w@mail.gmail.com

src/include/nodes/memnodes.h

@@ -120,7 +120,7 @@ typedef struct MemoryContextData
 
 	NodeTag		type;			/* identifies exact kind of context */
 	/* these two fields are placed here to minimize alignment wastage: */
-	bool		isReset;		/* T = no space alloced since last reset */
+	bool		isReset;		/* T = no space allocated since last reset */
 	bool		allowInCritSection; /* allow palloc in critical section */
 	Size		mem_allocated;	/* track memory allocated for this context */
 	const MemoryContextMethods *methods;	/* virtual function table */