Remove verb forms of "author" term (#319)

* Remove verb forms of "author" term

Styles are generally written expecting these terms to be empty. (cf. https://forums.zotero.org/discussion/116703/zotero-7-inserting-by-into-subsequent-cites#latest)

@adamsmith The author terms were added to zh-TW before they were added to the en-US locale, so I'm not sure whether to keep them. They are not included in the zh-CN locale. What do you think? 3f25b0c

* Remove author term from zh-TW locale

'作者' does not generally appear in traditional Chinese-locale publications

locales-en-US.xml

@@ -685,7 +685,6 @@
     </term>
 
     <!-- VERB ROLE FORMS -->
-    <term name="author" form="verb">by</term>
     <term name="chair" form="verb">chaired by</term>
     <term name="collection-editor" form="verb">edited by</term>
     <term name="compiler" form="verb">compiled by</term>

locales-pa-PK.xml

@@ -440,7 +440,6 @@
     </term>
 
     <!-- VERB ROLE FORMS -->
-    <term name="author" form="verb">بقلم</term>
     <term name="chair" form="verb">چیر نال</term>
     <term name="collection-editor" form="verb">سودھی نال</term>
     <term name="compiler" form="verb">مرتب نال</term>

locales-zh-TW.xml

@@ -433,7 +433,6 @@
       <single>series creator</single>
       <multiple>series creators</multiple>
     </term>
-    <term name="author">作者</term>     
     <term name="director">導演</term>     
     <term name="editor">編輯</term> 
     <term name="editorial-director">主編</term>     
@@ -485,7 +484,6 @@
       <single>cre.</single>
       <multiple>cres.</multiple>
     </term>
-    <term name="author" form="short">作者</term>     
     <term name="director" form="short">導演</term>     
     <term name="editor" form="short">編輯</term> 
     <term name="editorial-director" form="short">主編</term>     
@@ -511,7 +509,6 @@
     <term name="producer" form="verb">produced by</term>
     <term name="script-writer" form="verb">written by</term>
     <term name="series-creator" form="verb">created by</term>
-    <term name="author" form="verb">著</term>
     <term name="container-author" form="verb">著</term>
     <term name="director" form="verb">指導</term>
     <term name="editor" form="verb">編輯</term>